Radio communication system, radio communication apparatus, radio communication method, and computer program

ABSTRACT

An autonomously dispersed type wireless network is suitably formed with communication stations avoiding collision of beacons transmitted one to another. In the event that the range of reach of airwaves change and a receivable state is created and beacons collide, a communication station changes the beacon transmission position of itself in response to receiving a beacon from another station at a timing immediately prior to transmission to its own beacon. Also, in the event that beacon collision is exposed due to emergence of a new communication which can perform reception from two systems out of airwave range of each other, the newly-participating station requests one of the communication stations of which the beacons are colliding to change the beacon transmission timing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/472,990, filed May 16, 2012. U.S. application Ser. No. 13/472,990 isa continuation of Ser. No. 13/079,519, filed Apr. 4, 2011, now U.S. Pat.No. 8,199,737, issued Jun. 12, 2012. U.S. application Ser. No.13/079,519 is a continuation of U.S. application Ser. No. 10/569,426,filed Nov. 13, 2006, now U.S. Pat. No. 7,995,548, issued Aug. 9, 2011,the contents of which are incorporated herein by reference, and which isthe National Stage of PCT/JP04/14921, filed Oct. 8, 2004, and claimspriority to Japanese Patent Applications 2003-364230, filed Oct. 24,2003 and 2004-187106, filed Jun. 24, 2004.

TECHNICAL FIELD

The present invention relates to a wireless communication system, awireless communication device, a wireless communication method, and acomputer program, for performing mutual communication between multiplewireless stations such as with a wireless LAN (Local Area Network), andmore particularly relates to a wireless communication system, a wirelesscommunication device, a wireless communication method, and a computerprogram, wherein a wireless network is structured by the communicationstations operating in an autonomous distributed manner without anycontrolling-station/controlled-station relations.

More specifically, the present invention relates to a wirelesscommunication system, a wireless communication device, a wirelesscommunication method, and a computer program, wherein an autonomousdistributed wireless network is formed by the communication stationsnotifying one another at predetermined frame cycles with beaconsdescribing network information and the like, and particularly relates toa wireless communication system, a wireless communication device, awireless communication method, and a computer program, wherein anautonomous distributed wireless network is formed while avoidingcollision of beacons which the communication stations transmit one toanother.

Also, the present invention relates to a wireless communication system,a wireless communication device, a wireless communication method, and acomputer program, wherein the communication stations autonomouslyperform communication operations in increments of predetermined timeintervals, and more particularly relates to a wireless communicationsystem, a wireless communication device, a wireless communicationmethod, and a computer program, wherein the communication stationsperiodically transmit and receive signals each predetermined timeinterval while avoiding collision with signals of other stations.

BACKGROUND ART

The wireless LAN is gathering attention as a system to free users fromLAN cabling. With a wireless LAN, the greater part of cables can beomitted from the workspace such as offices and the like, socommunication terminals such as personal computers (PCs) can be movedwith relative ease. In recent years, increased speed and reduced processof wireless LAN systems has led to marked increase in demand thereof.Particularly, as of recent, introduction of the personal area network(PAN), wherein a small-scale wireless network is configured withmultiple electronic devices which people have nearby and communicationof information is performed, is being considered. Differing wirelesscommunication systems and wireless communication devices have beenstipulated, using frequency bandwidths which do not require licensing bythe regulatory authorities, such as the 2.4 GHz band and the 5 GHz band,for example.

An example of a commonplace standard relating to wireless networks isIEEE (The Institute of Electrical and Electronic Engineers) 802.11 (seeNon-patent Document 1, for example), Hiper LAN/2 (see Non-patentDocument 2 or Non-patent Document 3, for example), IEEE 802.15.3,Bluetooth communication, and so forth. Under the IEEE 802.11 Standard,various wireless communication methods exist according to thecommunication method and frequency band used, such as the IEEE 802.11aStandard, IEEE 802.11b Standard, and so on.

In order to configure a local area network using wireless techniques,with a commonly-used method, a device serving as a control station, thatis called an “access point” or “coordinator” is set up within the area,and a network is formed under the centralized control of this controlstation.

With a wireless network in which an access point has been set up, anaccess control method based on band reservation is widely employedwherein, in the event of transmission of information from a certaincommunication device, first, the band necessary for transmission of thatinformation is reserved at the access point so that transmission pathusage is implemented such that no collision with informationtransmission from other communication devices. That is to say, settingup the access point allows synchronous wireless communication whereincommunication devices within the wireless network are synchronized witheach other.

However, there is the problem with a wireless communication system whichhas an access point in that asynchronous communication betweentransmitting and receiving communication devices always necessitateswireless communication via the access point, meaning that the usageefficiency of the transmission path is halved.

As opposed to this, “Ad-hoc communication”, wherein communicationterminals directly perform asynchronous wireless communication, is beingproposed as another method for configuring a wireless network. Forsmall-scale wireless networks configured of a relatively small number ofclients which are in the proximity of each other in particular, ad-hoccommunication wherein arbitrary terminals can directly performasynchronous wireless communication without using a predetermined accesspoint is thought to be appropriate.

A central control station does not exist in an ad-hoc wirelesscommunication system, and accordingly is suitable for configuring a homenetwork made up of home electronic appliances, for example. Features ofan ad-hoc network are that the network does not readily fail since evenin the event that one device malfunctions or the power thereof is turnedoff, the routing is automatically changed, data can be transmitted overrelatively long distances while maintaining a high-speed data rate byhopping packets multiple times between mobile stations, and so forth.Various development examples of ad-hoc systems are known (see Non-patentDocument 4, for example).

For example, IEEE 802.11 wireless LAN systems have an ad-hoc mode foroperating peer-to-peer in an autonomous distributed manner without acontrol station begin provided. Under this operating mode, at the beacontransmission time each terminal counts a random period, and in the eventthat the device has not received a beacon from another terminal by thetime that the period ends, transmits its own beacon.

Now, conventional wireless networking will be described in detail withreference to the example of IEEE 802.11.

Networking with IEEE 802.11 is based on the concept of BSS (BasicService Set). There are two types of BSS; one being a BSS defined by aninfrastructure mode wherein a master such as an AP (Access Point:control station) exists, and an IBSS (Independent BSS) defined by anad-hoc mode configured only of multiple MTs (Mobile Terminals).

Infrastructure Mode

The operations of IEEE 802.11 when in the infrastructure mode will bedescribed with reference to FIG. 23. With an infrastructure mode BSS, anAP to perform coordination within the wireless communication system isindispensable.

The AP handles the range where the airwaves reach around itself as aBSS, thus configuring a “cell” as it is called in a so-called cellularsystem. An MT nearby the AP is contained in the AP, and participates inthe network as a member of the BSS. That is to say, the AP transmitscontrol signals called beacons at appropriate time intervals, the MTcapable of receiving these beacons recognizes that an AP is nearby, andfurther, a connection is established with the AP.

With the example shown in FIG. 23, the communication station the STA0operates as the AP, and the other communication stations the STA1 andthe STA2 operate as MTs. Now, as indicated in the chart to the rightside of the drawing, the communication station the STA0 serving as theAP transmits beacons a predetermined time intervals. The transmissionpoint-in-time of the next beacon is notified within the beacon by aparameter format known as Target Beacon Transmit Time (TBTT). Upon thetime of the TBTT coming, the AP operates beacon transmission procedures.

Conversely, by receiving the beacon, MTs nearby the AP can recognize thenext beacon transmission time by decoding of the internal TBTT field, soin some cases (in cases wherein there is no need for reception), thereceiving device may turn off the power and go to sleep until the nextor until several TBTTs in the future.

In the infrastructure mode, only the AP transmits beacons apredetermined frame cycles. On the other hand, the nearby MTs succeed inparticipating in the network by receiving the beacons form the AP, anddo not transmit beacons themselves. Note that the focus of the presentinvention is to operate a network without a master control station suchas an AP being directly involved, so the infrastructure mode will bediscussed no further.

Ad-hoc Mode

The operations of IEEE 802.11 when in the other ad-hoc mode will bedescribed with reference to FIG. 24.

With IBSS in the ad-hoc mode, multiple MTs perform negotiation one withanother, and subsequently autonomously define the IBSS. Upon definingthe IBSS, at the end of the negotiation the MT group determines the TBTTevery predetermined interval. Upon recognizing that the TBTT has arrivedby referencing a clock within itself, following a random time delay eachMT transmits a beacon in the event of recognizing that no one hastransmitted a beacon yet.

In the example shown in FIG. 24, the manner in which two MTs make up anIBBS is illustrated. In this case, one of the MTs belonging to the IBSStransmits a beacon each time the TBTT arrives. This also includes caseswherein beacons transmitted from the MTs collide.

There are also cases with IBSS wherein the MTs turn off the power of thetransmitting/receiving device and go to sleep as necessary. However, thesleep state is not directly related to the essence of the presentinvention, and accordingly description thereof will be omitted in thepresent specification.

Transmission/Reception Procedures Under IEEE 802.11

Next, transmission/reception procedures under IEEE 802.11 will bedescribed.

It is know that with wireless LAN networks under an ad-hoc environment,a hidden terminal problem generally occurs. A hidden terminal is aterminal which can be heard from one communication station which is theother part of communication therewith in a case of communication beingcarried out between certain communication stations, but cannot be heardby other communication stations, and since negotiation cannot beperformed between hidden terminals, there is the possibility thattransmission operations may collide.

CSMA/CA according to RTS/CTS procedures is known as a methodology forsolving the hidden terminal problem. IEEE 802.11 also employs thismethodology.

Now, CSMA (Carrier Sense Multiple Access with Collision Avoidance:Carrier Sense Multiple Access) is a connection method for performingmultiple access based on carrier detection. Since receiving signals ofinformation transmitted from a local station is difficult in wirelesscommunication, collision is avoided by starting information transmissionfrom the local station following confirming that there is no informationtransmission from other communication devices with the CSMA/CA(Collision Avoidance) method rather than CSMA/CD (Collision Detection).The CSMA method is an access method suitable for asynchronous datacommunication such as file transfer and electronic mail.

With the RTS/CTS method, transmission of data is started in response toa communication station which is the data originator transmitting atransmission request packet RTS (Request To Send), and a confirmationnotification packet CTS (Clear To Send) being received form thecommunication station which is the data transmission destination. Upon ahidden terminal receiving at least one of an RTS or CTS, a transmissionstop period is set of the local station for a period during which datatransmission based on RTS/CTS procedures is predicted, whereby collisioncan be avoided.

FIG. 25 illustrates an operation example of RTS/CTS procedures. With theexample shown in the drawing, an example is illustrated of a casewherein information (Data) is transmitted from a communication stationthe STA0 to a communication station the STA1 which mutually performcommunication operations in an autonomously dispersed manner.

First, prior to actual information transmission, the STA0 confirms thatthe media is clear for a predetermined time, following which the RTSpacket is transmitted to the STA1, which is the destination of theinformation, following CSMA procedures. In response o reception of theRTS packet, the STA1 transmits a CTS packet to the STA0 which givesfeedback to the effect that the RTS has been received.

In the event that the CTS is successfully received, the STA0 which isthe transmitting side determines that the media is clear, and promptlytransmits the information (Data) packet. Also, upon successfullyreceiving the information, the STA1 returns an ACK, whereby one packetof RTS/CTS transmission/reception transaction ends.

In the event that another station has happened to have transmitted somesort of signal at the same time as the STA0 which is the informationoriginator transmitting the RTS, the STA1 which is the informationrecipient cannot receive the RTS due to the signals colliding. In thiscase, the STA1 does not return a CTS. As a result, the STA0 canrecognize that the earlier RTS has collided, since no CTS is receivedfor a while. Then, procedures for resending the RTS with a randombackoff are activated at the STA0. Basically, competition is carried outfor wining transmission rights while bearing the risk of such collision.

Access Competition Method in IEEE 802.11

Next, the access competition method stipulated in IEEE 802.11 will bedescribed.

With IEEE 802.11, four types of packet intervals (IFS: Inter FrameSpace) are defined. Here, three of these IFSs will be described withreference to FIG. 26. The IFSs defined are, in order from the shorter,SIFS (Short IFS), PIFS (PCF IFS), and DIFS (DCF IFS).

With IEEE 802.11, CSMA is employed as a basic media access procedures(described above), however, it should be noted that a transmission rightis granted to the transmitting device only in a case wherein a backofftimer is operated over a random time period while monitoring the mediastate before transmitting something, and there are no signalstransmitted during this period.

In the case of transmitting normal packets following the CSMA procedures(DCF (called Distributed Coordination Function), following some sort ofpacket transmission ending, first, the media state is monitored by DIFS,and in the event that there are no transmission signals during thisperiod, a random backoff is taken, and further, in the event that thereare no transmission signals during this period as well, transmissionrights are granted.

On the other hand, transmission of packets with extraordinarily highurgency, such as ACK, is permitted following SIFS packet intervals. Thisenables packets with high urgency to be transmitted before packetstransmitted following normal CSMA procedures.

To summarize the above, the reason that differing types of packetinterval IFSs are defined is that prioritizing is performed in thepacket transmission competition, according to whether the IFS is SIFS,PIFS, of DIFS, i.e., according to the packet interval length. Thepurpose of using PIFS will be described later.

Band Guarantee (1) Under IEEE 802.11

In a case of access competition with CSMA, guaranteeing and securing acertain band is impossible. Accordingly, IEEE 802.11 has PCF (PointCoordination Function) to serve as a mechanism for guaranteeing andsecuring a band. However, PCF is based on poling, and does not operateunder Ad-hoc but is only performed under management of an AP in theinfrastructure mode.

FIG. 27 illustrates the way in which preferential communication isprovided by PCF operations. In the drawing, the STA0 operates as an AP,and the STA1 and the STA2 participate in the BSS managed by the AP. Thiscase assumes the STA1 transmitting information while guaranteeing band.

After transmitting a beacon for example, the STA0 serving as the APperforms poling by transmitting a CF-Poll message to the STA1 at a SIFSinterval. The STA1 which has received the CF-Poll is granted datatransmission rights, and transmission of data at the SIFTS interval ispermitted, in response to this, the STA1 transmits data following SIFS.Upon the STA0 returning an ACK to the transmitted data, and onetransaction ending, the STA0 polls the STA1 again.

In the example shown in FIG. 27, a case wherein this poling has failedfor some reason is shown. At this time, upon recognizing thatinformation is not transmitted from the STA1 following SIFS after polingthe STA1 again, the STA0 deems the poling to have failed, and performspoling again following a PIFS interval. In the event that the polingretry succeeds, data is transmitted from the STA1, and an ACK isreturned from the STA0.

Even in the event that the STA2 has a transmitted packet, for example,during this series of procedures, the transmission right never shifts tothe STA2, since this would mean that the STA0 or the STA1 would betransmitting at a SIFS or PIFS interval before the DIFS time intervalelapses. That is to say, the STA1, which has been polled by the STA0serving as the AP, always has the transmission right.

Band Guarantee (2) Under IEEE 802.11

Further band guarantee means are being studied for IEEE 802.11, andimplementation of a technique called Enhanced DCF (EDCF) is planned (theQoS enhancement in IEEE 802.11e). EDCF is arranged such that the widthfor which a random backoff value can be set is short for urgent trafficneeding band guarantee, and the width for which the packet intervals IFSand backoff value shown in FIG. 26 can be set is longer for othertraffic. Consequently, a mechanism is realized which enablestransmission of urgent traffic in a statistical manner, though not asconclusive as with PCF.

FIG. 28 illustrates the manner in which preferential transmission isprovided to traffic regarding which EDCF operations guarantee band. Inthe example shown in the drawings, a case is assumed wherein the STA1attempts to transmit preferential traffic to the STA0, and the STA2attempts to transmit non-preferential traffic to the STA0. Also, thestandard IFS for both traffics is assumed to be time equivalent to DIFS.

Upon the media becoming clear from point-in-time T0, the STA1 and theSTA2 both wait for the time of DIFS to elapse. The media is still clearfollowing DIFS elapsing from T0 (point-in-time T1), so the STA1 and theSTA2 both start to confirm that the media is clear at a time determinedby random backoff.

With EDCF operations, the backoff value of the STA1 is short forpreferential traffic, and the backoff value of the STA2 is long fornon-preferential traffic. FIG. 28 illustrates the backoff values frompoint-in-time T1 of each of the communication stations with arrows. Atpoint-in-time T2 where time of the backoff value of the STA1 haselapsed, the STA1 starts transmission of the RTS. On the other hand, theSTA2 detects the RTS transmitted from the STA1, updates the backoffvalue, and prepares for the subsequent transmission.

Also, the STA0 returns a CTS at point-in-time T3 where SIFS has elapsedfrom reception of the RTS. The STA1 which has received the CTS startsdata transmission at a point-in-time T4 where SIFS has elapsed fromreception of CTS. The STA0 then returns an ACK at a point-in-time T5where SIFS has elapsed from reception of data from the STA1.

At point-in-time T6 where returning of the ACK by the STA0 ends, themedia is clear again. The STA1 and the STA2 both await elapsing of timeof DIFS again. In the event that the media is still clear followingelapsing of DIFS (point-in-time T7), the STA1 and the STA2 both start toconfirm that the media is clear at a time determined by random backoff.Here also, the backoff value of the STA1 is set short due topreferential traffic, and RTS transmission is performed before thebackoff value of the STA2 at point-in-time T8.

Due to the above-described procedures, order of access rights isprovided to the STA1 and the STA2 competing for the access right,according to the degree of preference of the traffic being handled.Also, though not shown in the drawing, the backoff value of the STA2also gradually becomes shorter, so a situation wherein the STA2 nevergets access rights does not occur.

[Non-Patent Document 1]

-   International Standard ISO/IEC 8802-11:1999(E) ANSI/IEEE Std.    802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control    (MAC) and Physical Layer (PHY) Specifications    [Non-Patent Document 2]-   ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Radio Access    Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer;    Part 1: Basic Data Transport Functions    [Non-Patent Document 3]-   ETSI TS 101 761-2 V1.3.1 Broadband Radio Access Networks (BRAN);    HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 2: Radio Link    Control (RLC) sublayer    [Non-Patent Document 4]-   “Ad Hoc Mobile Wireless Network” by C. K. Tho (published by Prentice    Hall PTR)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

As described above, while the transmission/reception proceduresaccording to IEEE 802.11 enable the problems of access competition andband guarantee to be solved, there are several problems which remain,which are listed below.

(1) Existence of Point Coordinator

As described above, IEEE 802.11 provides a mechanism for QoScommunication by PCF. However, PCF operates under the presence of an APwhich centrally governs media access. With a network having an AP,malfunctioning at the AP causes a problem that all communication becomesunavailable. Also, there is the problem that MTs which are at locationswhere communication with the AP cannot be made, cannot participate inthe network.

(2) Problem of Increased Probability of collision with EDFC

With the mechanism of EDCF in IEEE 802.11, links with higher preferencebasically can be preferentially passed even without a Point Coordinatorsuch as an AP. However, in the event that multiple stationssimultaneously start transmission with high preference, collisionsfrequently occur since the backoff is set short, leading to the problemof lowered communication efficiency. Also, there are cases where trafficwith low preference is set with long IFSs, and under an environmentwherein traffic with lower preference is dominant, the transmissionright competition is performed following elapsing of long IFSs for allcommunication stations, leading to the problem that the overhead isgreat and communication efficiency drops. Moreover, in a case whereinthere is no control station such as an AP, there is no say to suppressrequests for traffic exceeding the capacity load of the network, leadingto the program not requests form higher order layers cannot be fulfilledat all links. In cases where multiple video streams and the like areprovided, this emerges as a great problem.

(3) Problem of Beacon Collision

At the time of configuring a network, a predetermined control station orcommunication stations operating in an autonomously dispersed mannerperform notification at predetermined intervals with beacons describingnetwork information and the like. There is the problem of beaconcollision in such systems. For example, with IEEE 802.11, this problemsoccurs in the case of performing beacon transmission from multiplestations in the same area and on the same channel, in both theinfrastructure mode and the Ad-hoc mode.

In the Ad-hoc mode, the beacon transmission stations are defined withrandom backoff to begin with, so beacon collision is unavoidable fromthe beginning. Also, with the infrastructure mode, while there is noproblem in the event that only a single BSS exists, multiple beaconscoexist in a case wherein multiple BSSs enter the airwave range due tothe network relocating or a nearby airwave-blocking object moving. Inthe event that the beacon transmission time overlaps here, a problemoccurs in that the nearby stations cannot receive the beacons.

The present invention has been made in light of the above-describedtechnical problems, and accordingly, it is a primary object thereof toprovide a superior wireless communication system, wireless communicationdevice, wireless communication method, and computer program, wherein awireless network is formed by communication stations operating in anautonomous distributed manner without a device serving as a controlstation being disposed.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein an autonomousdistributed network with guaranteed quality of communication can beconstructed without involvement of a specified control station.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein data transmissioncan be performed while avoiding collision in an autonomous distributednetwork without involvement of a specified control station.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein beacon collision canbe appropriately avoided among multiple communication stations in anetwork configured by communication stations performing notificationwith beacons.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein an autonomousdispersed wireless network can be suitably formed while avoidingcollision of beacons which the communication stations transmit one toanother.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein the communicationstations each can autonomously perform suitable autonomous communicationoperations in time interval units.

It is a further object of the present invention to provide a superiorwireless communication system, wireless communication device, wirelesscommunication method, and computer program, wherein a communicationstation can perform periodic signal transmission and reception at eachpredetermined time interval, while avoiding collision with signals ofother stations.

Means for Solving the Problems

The present invention has been made in light of the above problems, anda first aspect thereof is an autonomous dispersed type wirelesscommunication system for constructing a network by communicationstations transmitting beacons describing network-related information toeach other at predetermined time intervals, with no particular controlstation installed; wherein collision of beacons transmitted from two ormore communication stations within the network is detected; and whereincollisions are resolved by changing the transmission timing of at leastone of the beacons, in response to detection of the collision.

Note however, that “system” as used here refers to a logical collectionof multiple devices (or functional modules for realizing certainfunctions), and whether each of the devices and functional modules arein a single housing is of no particular concern.

Under an autonomous dispersed communication environment, eachcommunication station performs notification of beacon information atpredetermined time intervals, thereby announcing its own existence toother neighboring (i.e., within a communicable range) communicationstations, and also notifies the network configuration. Also, thecommunication stations perform scanning operations for each channel andreceive beacon signals, thereby detecting penetration of thecommunication range of a neighboring station, and also enables knowingthe network configuration by analyzing the information described in thebeacon.

Also, each communication station includes and transmits, in beaconsignals, neighboring device information relating to beacon transmissiontiming. In this case, the communication station can obtain not onlynetwork information of the neighboring station from which beacons can bedirectly received, but also beacon information relating to a station thenext over, i.e., a hidden terminal, which the local station cannotreceive beacons from but the neighboring station can.

With such an autonomous dispersed network, communication station newlyparticipating first perform scanning operations, i.e., continuouslyattempt signal reception for a period equal to or lower than a superframe, and confirm existence of beacons transmitted by the nearbystations. In the event that no beacons are received from the nearbystations in this process, the communication station sets an appropriatebeacon transmission timing. On the other hand, in the case that beaconstransmitted from nearby stations are received, the neighboring deviceinformation described in each of the received beacons is referred to soas to set a timing at which none of the already-existing stationstransmit beacons, as the beacon transmission timing of the localstation.

Under conditions wherein the communication stations are each stationaryand the airwave permeation range does not change, beacon collision canbe avoided by the above-described procedures. On the other hand, in theevent that the airwave permeation range changes due to the communicationstation moving or the like, cases can occur wherein beacons transmittedby the communication stations collide.

For example, in a case wherein communication stations of two systems outof range of the airwaves of each other set the same transmission timingcompletely independent of each other, but then move into an airwavepermeation range so that airwaves of each are receivable, a statewherein the beacons of the stations collide occurs.

Or, a case is also conceivable wherein, following communication stationsof two systems out of range of the airwaves of each other setting thesame transmission timing completely independent of each other, a newcommunication station which is capable of reception from both systemsemerges, thereby exposing collision of beacons transmitted by each ofthe communication stations.

According to the present invention, upon detection of collision ofbeacons transmitted from two or more communication stations within acommunication range, collision of beacons is avoided by autonomousactions of each of the communication stations, by changing thetransmission timing of at least one of the beacons.

Here, the communication station which changes the beacon transmissiontiming notifies nearby stations with a beacon describing a warning tothe effect that the beacon transmission timing is to be changed,performs a scanning operation for at least a predetermined period,discovers a timing which is not being used for beacon transmission bynearby stations, and determines this to be a new beacon transmissiontiming.

In a case wherein communication stations of two systems out of range ofthe airwaves of each other set the same transmission timing completelyindependent of each other, but then move into an airwave permeationrange so that airwaves of each are receivable, collision of the beaconsof each other can be recognized between the communication stations.

In such a case, collision can be avoided by one of the communicationstations autonomously moving the beacon transmission timing of itself.For example, in response to receiving a beacon of another station at atiming which may result in collision immediately prior to transmissionof a beacon from itself, the communication station changes the beacontransmission position of itself. Or, in response to receiving a beaconof another station at a timing which may result in collision immediatelyfollowing transmission of a beacon from itself, the communicationstation changes the beacon transmission position of itself.

Or, an arrangement may be made wherein, instead of one communicationstation autonomously changing the beacon transmission timing, acommunication station requests the other station to change the beacontransmission timing upon recognizing collision of beacons from receivingbeacons of another station at a timing close to that of its own beacontransmission timing.

Also, in a case wherein, following communication stations of two systemsout of range of the airwaves of each other setting the same transmissiontiming completely independent of each other, a new communication stationwhich is capable of reception from both systems emerges, therebyexposing collision of beacons transmitted by each of the communicationstations, the newly-participating station may request one of thecommunication stations with which beacons are colliding to change thebeacon transmission timing. Changing the beacon transmission timing asused here includes stopping beacon transmission, as well as moving thebeacon transmission timing.

Now, with the wireless communication network according to the presentinformation, the communication stations win preferential usage periodsfor traffic due to having transmitted beacons. An arrangement may bemade wherein the communication stations each transmit a regular beaconjust once, and also transmit one or more auxiliary beacons made up ofsignals similar to the regular beacon, at the predetermined timeintervals.

For example, traffic priority is set in the auxiliary beaconstransmitted by the communication stations, and notification is made withthe beacons describing priority-related information. In this case, anarrangement may be made wherein, in the event that beacon collisionoccurs, the priority of each others beacons is referred, and theoriginator of the beacon with the lower priority changes it own beacontransmission timing. Changing the beacon transmission timing as usedhere includes stopping beacon transmission, as well as moving the beacontransmission timing.

Also, in the event that a communication station with which beacons arecolliding is equivalent to a hidden station, beacons cannot be directlyreceived, so the priority cannot be compared with the beacon of thelocal station.

In such a case, the communication station transmits a beacon stoprequest toward nearby stations, specifying the number of beacons whichthe communication station wants to place within the predetermined timeinterval, and the priorities thereof. On the other hand, thecommunication stations which have received the beacon stop requestdetect beacons with priority of or lower than that specified in thepredetermined time interval, of a number equal to that specified, andtransmit a beacon stop request to each of the beacon-originatingcommunication stations. Due to such remote operations, the communicationstation can obtain the desired beacon transmission timing from hiddenterminals, in the same way as with neighboring stations which canmutually receive beacons.

Also, a second aspect of the present invention is a wirelesscommunication system for constructing a network by communicationstations performing periodic communication operations at eachpredetermined time interval, with nocontrolling-station/controlled-station relations; wherein, in the eventof performing periodic signal transmission/reception at each thepredetermined time interval, a communication station attempts receptionof transmission signals from other stations at least at one of prior tothe periodic signal transmission/reception and following the periodicsignal transmission/reception, so as to detect whether or not there iscollision between the periodic signal transmission/reception andtransmission signals of other stations.

With the wireless communication system according to the second aspect ofthe present invention, under an autonomous dispersed communicationenvironment wherein each communication station autonomously performsperiodic communication operations at predetermined time intervals, acommunication station is permitted to obtain a reserved band orpreferential usage period at a suitable timing within the predeterminedtime interval, and perform periodic communication operations at eachpredetermined time interval.

In the case of performing periodic transmission/reception operations ateach predetermined time interval, the communication station attemptsreception of a transmission signal from another station prior toperiodic signal transmission/reception or following signaltransmission/reception, so as to detect whether or not there iscollision between the periodic signal transmission/reception and thesignal transmission of the other station. Specifically, receivingtransmitted signals of the other station at a timing near that of theperiodic signal transmission/reception timing of the local stationenables collision at the periodic signal transmission/reception timingto be detected. Also, receiving periodic transmitted signals of theother station at a timing near that of the signal transmission/receptiontiming of the local station enables collision at the periodic signaltransmission/reception timing to be detected.

Also, an arrangement may be made wherein, a communication stationperforms scanning processing for at least a predetermined period inresponse to detection of collision of the periodictransmission/reception signals, thereby attempting confirmation of thestate of cyclic signal transmission of other stations.

Now, the communication station may attempt reception of a transmissionsignal from another station prior to periodic signaltransmission/reception, wherein, in response to detection of collisionbetween the periodic signal transmission/reception and the signaltransmission of the other station, the signal transmission timing of thelocal station is delayed, so as to avoid collision with the signals ofthe other station, thereby avoiding collision.

In such a case, the communication station may transmit signals withdescription to the effect that the periodic signal transmission timinghas been changed to avoid collision. The other station with whichcollision has occurred receives signals with description to the effectthat the periodic signal transmission timing has been changed to avoidcollision, and can detect collision with the periodic signals which wereto be transmitted following transmission by the local station.

Also, the communication stations may notify each other with beacons withdescription of the schedule of signals to be periodicallytransmitted/received. In this case, the communication stations canextract the periodic signal transmission/reception point-in-time of eachother. In the event of detecting collision in a periodic signaltransmission/reception section based on information described in abeacon received from a nearby station, the colliding signaltransmission/reception timing can be changed.

Also, the communication station may set an order of preference tosignals periodically transmitted/received, and make notification withbeacons describing has a preferential order along with a schedule ofsignals periodically transmitted/received. Upon detecting collision in aperiodic signal transmission/reception section based on informationdescribed in beacons received from nearby stations, collision can beavoided by changing the timing of the periodically transmitted/receivedsignals with lower preferential order.

Also, a communication station may describe relative point-in-timeinformation from the beacon transmission point-in-time of thecommunication station in a part of signals periodicallytransmitted/received. In this case, upon receivingperiodically-transmitted signals transmitted by other stations, thecommunication station can extract the transmission point-in-time of thetransmitting station of the signal, based on the relative point-in-timeinformation from the beacon transmission point-in-time described in thesignals periodically transmitted, and detect collision. Stoppingtransmission of other signals performed at the point-in-time allowscollision to be avoided.

Also, an arrangement may be made wherein the communication stationdescribes, in a part of signals periodically transmitted, information tothe effect that the signals are being periodically scheduled andtransmitted. Further, information may be described in a part of thesignals periodically transmitted, indicating the preferential order ofthe signals. In such a case, the communication station can change theperiodic signal transmission/reception timing with lower priority order,in response to detection of collision of periodic signaltransmission/reception.

Also, the communication station may attach a random offset to thetransmission point-in-time for the periodic signaltransmission/reception. The communication station may describeinformation relating to the random offset of the transmissionpoint-in-time in part of the signals periodically transmitted/received.

Also, the communication station may extract a time span in whichcollision with periodic signal transmission/reception of other stationswill not occur by performing a scanning operation prior to newlygenerating periodic signal transmission/reception, and set the newperiodic signal transmission/reception timing to the time span in whichcollision with periodic signal transmission/reception of other stationswill not occur.

Also, at the time of performing a scanning operation for obtaininginformation relating to a network, the communication station may extracta time span in which information necessary for obtaining the informationis transmitted, and attempt signal reception in the extracted time slot,so as to efficiently perform scanning operations.

Also, at the time of acquiring one or more periodic signaltransmission/reception sections and performing transmission/receptionwith a desired communication station, the communication station maymonitor the signal reception state in periodic signaltransmission/reception sections. Also, periodic signaltransmission/reception sections, regarding which marked deterioration inthe signal reception state has been detected, may be released, since itcan be estimated that collision with other signals is occurring.

Also, the communication station may performs signaltransmission/reception based on access procedures following the CSMAmethod involving signal detection for a predetermined time on atransport path and standby for a random back-off period, in a time spanother than periodic signal transmission/reception sections of nearbystations.

Also, a third aspect of the present invention is a wirelesscommunication system for constructing a network by communicationstations transmitting beacons describing network-related information toeach other at predetermined time intervals, with nocontrolling-station/controlled-station relations; wherein, in the eventof performing periodic signal transmission/reception at each thepredetermined time interval, a communication station describes relativepoint-in-time information from the beacon transmission point-in-time ofthe communication station, in a part of signals periodicallytransmitted/received, and collision between beacons of nearby stationsand signals transmitted and received by other stations is detected basedon relative point-in-time information described in signals received fromnearby stations.

With the wireless communication system according to the third aspectaccording to the present invention, a network is constructed bycommunication stations periodically notifying each other with beacons. Acommunication station is permitted to obtain a reserved band orpreferential usage period at a suitable timing within the predeterminedtime interval, and perform periodic communication operations at eachpredetermined time interval.

Now, collision can be detected between communication stations can bedetected by the communication stations, which periodically performcommunication operations ever predetermined time interval, describingrelative point-in-time information from the beacon transmissionpoint-in-time in a part of the singles periodicallytransmitted/received. Specifically, the communication station mayextract the transmission point-in-time of beacons of nearby stations,based on relative point-in-time information described in the signalsreceived from the nearby stations, and detect collision with beacons ofthe nearby stations in the event that a signal has been transmitted fromthe local station at the same point-in-time.

Also, the communication station may extract the transmissionpoint-in-time of beacons of nearby stations, based on relativepoint-in-time information described in the signals received from thenearby stations, and detect collision with beacons of the nearbystations in the event that signals cannot be received from the otherstation at the same point-in-time.

Also, the communication station may avoid collision in response todetection of collision of signals. For example, the communicationstation may avoid collision by stopping transmission of other signalsperformed at the beacon signal transmission point-in-time that has beenextracted.

Also, a fourth aspect of the present invention is a computer programdescribed in a computer-readable format so as to execute, on a computersystem, processing for performing wireless communication operationsunder an autonomously dispersed communication environment constructed bycommunication stations transmitting beacons describing network-relatedinformation to each other at predetermined time intervals, with nocontrolling-station/controlled-station relations, the programcomprising: a beacon signal generating step for generating beaconsignals describing information relating to a local station; a beaconsignal analyzing step for analyzing beacon signals received from nearbystations; a timing control step for controlling the beacon transmissiontiming; and a collision avoiding step for avoiding beacon collisionsoccurring with other stations.

Also, a fourth aspect of the present invention is a computer programdescribed in a computer-readable format so as to execute, on a computersystem, processing for performing communication operations at eachpredetermined time interval, under a communication environment with nocontrolling-station/controlled-station relations, the programcomprising: a signal transmission/reception step for performing periodicsignal transmission/reception at each the predetermined time interval;and a collision detecting step for attempting reception of transmissionsignals from other stations at least at one of prior to the periodicsignal transmission/reception and following the periodic signaltransmission/reception, so as to detect whether or not there iscollision between the periodic signal transmission/reception andtransmission signals of other stations.

Also, a fifth aspect of the present invention is a computer programdescribed in a computer-readable format so as to execute, on a computersystem, processing for performing wireless communication operationsunder a communication environment constructed by communication stationstransmitting beacons describing network-related information to eachother at predetermined time intervals, with nocontrolling-station/controlled-station relations, the programcomprising: a beacon signal generating step for generating beaconsignals describing information relating to a local station; a beaconsignal analyzing step for analyzing beacon signals received from nearbystations; a signal transmission/reception step for describing, in a partof signals, relative point-in-time information from the beacontransmission point-in-time, and performing periodic signaltransmission/reception at each the predetermined time interval; and acollision detecting step for detecting collision between a beacon from anearby station and signals transmitted/received by other stations, basedon the relative point-in-time information described in the signalsreceived from the nearby station.

The computer programs according to the fourth through sixth aspects ofthe present invention define computer programs described in acomputer-readable format so as to realize predetermined progressing of acomputer system. In other words, installing the computer programsaccording to the fourth through sixth aspects of the present inventionin a computer system causes the computer system to exhibit cooperativeactions, and to operate as a wireless communication device. Activating aplurality of such wireless communication devices and configuring awireless network yields the same advantages as those of the wirelesscommunication system according to the first through third aspects of thepresent invention.

Advantages

According to the present invention, a superior wireless communicationsystem, wireless communication device, wireless communication method,and computer program, wherein a network is formed by communicationstations operating in an autonomous distributed manner without a deviceserving as a control station being disposed, can be provided.

Also, according to the present invention, a superior wirelesscommunication system, wireless communication device, wirelesscommunication method, and computer program, wherein data transmissioncan be performed while avoiding collision in an autonomous distributedwireless network without involvement of a specified control station, canbe provided.

Also, according to the present invention, a superior wirelesscommunication system, wireless communication device, wirelesscommunication method, and computer program, wherein beacon collision canbe appropriately avoided among multiple communication stations in anetwork configured by communication stations performing notificationwith beacons, can be provided.

Also, according to the present invention, a superior wirelesscommunication system, wireless communication device, wirelesscommunication method, and computer program, wherein an autonomousdispersed wireless network can be suitably formed while avoidingcollision of beacons which the communication stations transmit one toanother, can be provided.

Also, according to the present invention, a superior wirelesscommunication system, wireless communication device, wirelesscommunication method, and computer program, wherein the communicationstations each can autonomously perform suitable communication operationsat predetermined time interval units, can be provided.

Also, according to the present invention, a superior wirelesscommunication system, wireless communication device, wirelesscommunication method, and computer program, wherein a communicationstation can perform periodic signal transmission and reception at eachpredetermined time interval, while avoiding collision with signals ofother stations, can be provided.

According to the present invention, QoS communication can be providedeven under a dispersed control environment where no Point Coordinatorsuch as a control station exists. Also, each of the communicationstations can autonomously understand the network load even under adispersed control environment, so in the event that traffic exceedingthe capacity load of the network is requested, just traffic with lowpreferential order can be eliminated according to the preferential orderwhich the upper layer of the communication protocol requests.

Also, according to the present invention, situations wherein beaconcollision continuously occurs can be avoided even incases of beaconcollision due to networks crossing or the like, and the presence of eachnode existing in the network can be understood in a sure manner, so thesuppression in occurrence of connection cut-offs and the like can bemarkedly improved.

Other objects, features, and advantages of the present invention willbecome more apparent from the later-described embodiments of the presentinvention and detailed description made with reference to the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a placement example of communicationdevices configuring a wireless communication system according to anembodiment of the present invention.

FIG. 2 is a diagram schematically illustrating the functionconfiguration of a wireless communication device operating as acommunication station in a wireless network according to an embodimentof the present invention.

FIG. 3 is a diagram for describing the procedures for each of thecommunication stations to transmit beacons in an autonomously dispersednetwork according to the present invention.

FIG. 4 is a diagram illustrating a configuration example of beacontransmission timings which can be placed within a super frame cycle.

FIG. 5 is a diagram illustrating the manner in which a beacontransmission station is given preferential rights within a super framecycle.

FIG. 6 is a diagram illustrating the configuration of a super framecycle.

FIG. 7 is a diagram illustrating an example of the format of a beaconframe transmitted in the autonomously dispersed type wirelesscommunication system according to the present embodiment.

FIG. 8 is a diagram for describing TBTT offset.

FIG. 9 is a diagram for describing procedures for a newly-participatingcommunication station to set TBTTs for itself based on the NBOIs ofbeacons obtained from beacons received from nearby stations.

FIGS. 10A-10D are diagrams illustrating the way in which beacons collidedue to change in the range of reach of airwaves.

FIG. 11 is a diagram illustrating an example of TBTT changingprocedures.

FIG. 12 is a diagram illustrating a modification of the TBTT changingprocedures shown in FIG. 11.

FIG. 13 is a flowchart illustrating device operations executed at eachcommunication station in order to avoid beacon collision upon beaconcollision occurring due to change in the range of reach of airwaves orthe like, by one of the communication stations of which the beacon hascollided changing the beacon transmission point-in-time (TBTT change).

FIGS. 14A-14D are diagrams illustrating the manner in which collision ofbeacons transmitted by the communication stations is exposed due topower of a new communication station being turned on.

FIG. 15 is a diagram illustrating an example of TBTT changing proceduresin the event that collision of beacons being exposed due toparticipation of a new communication station.

FIG. 16 is a flowchart illustrating device operations executed at eachcommunication station in order to avoid beacon collision upon beaconcollision occurring due to emergence of a newly-participating station,by requesting one of the communication stations of which the beacon hascollided to change the beacon transmission point-in-time (TBTT change).

FIG. 17 is a flowchart illustrating procedures for a communicationstation to set a new TBTT within the super frame cycle.

FIG. 18 is a diagram for describing the procedures for searching thebeacons with TBTTs placed within a super frame for those with low orderof preference, and setting TBTTs for the local station.

FIG. 19 is a diagram illustrating the manner in which a communicationstation eliminates low order of preference beacons of other stations ina state wherein the super frame is full of beacons with TBTTs alreadyset, and sets a new TBTT.

FIG. 20 is a diagram illustrating the manner in which a communicationstation which desires to set a TBTT for a new beacon stops beacontransmission by remote operations via nearby stations, and sets TBTTsfor itself.

FIG. 21 is a diagram illustrating the manner in which a communicationstation which desires to set a TBTT for a new beacon stops beacontransmission by remote operations via nearby stations, and sets TBTTsfor itself.

FIG. 22 is a diagram schematically illustrating the configuration of anALERT field.

FIG. 23 is a diagram for describing the operations in a wireless networkbased on IEEE 802.11 in the infrastructure mode.

FIG. 24 is a diagram for describing the operations in a wireless networkbased on IEEE 802.11 in the ad-hoc mode.

FIG. 25 is a chart illustrating an example of access operations byRTS/CTS procedures.

FIG. 26 is a diagram illustrating packet interval IFS defined in IEEE802.11.

FIG. 27 is a diagram for describing PCF (Point Coordination Function)operations.

FIG. 28 is a diagram illustrating the way in which preferentialtransmission is provided to band-ensured traffic by EDCF operations.

FIG. 29 is a diagram for describing operations for a communicationstation to start transmission in each of a TPP section and FAP section.

FIG. 30 is a diagram illustrating the manner in which a communicationstation increases preferential usage period by transmitting multiplevirtual beacons called auxiliary beacons.

FIG. 31 is a diagram illustrating a state transition diagram of awireless communication device operating as a communication station.

FIG. 32 is a diagram illustrating state transition of a wirelesscommunication device operating as a communication station.

FIG. 33 is a diagram for describing collision detection means in a casewherein beacons of communication stations transmitting and receivingdata have collided.

FIG. 34 is a diagram for describing collision detection means in a casewherein beacons of communication stations transmitting and receivingdata have collided.

FIG. 35 is a diagram for describing collision detection means in a casewherein beacons of communication stations transmitting and receivingdata have collided.

FIG. 36 is a diagram for describing collision detection means in a casewherein beacons of communication stations transmitting and receivingdata have collided.

FIG. 37 is a diagram for describing collision detection means in a casewherein beacons of communication stations transmitting and receivingdata have collided.

FIG. 38 is a flowchart illustrating communication procedures includingcollision avoiding operations in a case wherein, in addition to theTBTTs of colliding signals matching, even the random values thereof havecompletely matched.

FIG. 39 is a diagram illustrating an example of communication operationsfor performing signal collision avoidance based on the contentsdescribed in the Serial field appended to an auxiliary beacon orperiodically-transmitted signals.

FIG. 40 is a diagram illustrating an example of communication operationsfor performing signal collision avoidance based on the contentsdescribed in the Serial field appended to an auxiliary beacon orperiodically-transmitted signals.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings.

A. System Configuration

The communication transmission path serving as the basis for the presentinvention is wireless, with multiple communication stations configuringa network. The communication serving as the basis for the presentinvention is storage exchange type traffic, with information beingtransferred in increments of packets. Also, while the followingdescription assumes that each communication station handles a singlechannel, this can be expanded to an arrangement wherein multiplefrequency channels are used, i.e. multi-channel transmission media isused.

The wireless network system according to the present invention is anautonomously dispersed system configuration wherein a coordinator is notprovided, and transmission control effectively using channel resourcesby transmission (MAC) frames having a loose time-divisionmultiple-access structure is performed. Also, the communication stationscan also perform ad-hoc communication wherein information is directlyasynchronously transmitted following access procedures based on CSMA.

With such an autonomously dispersed wireless communication systemwherein a control station is not provided in particular, eachcommunication station notifying beacon information on the channelnotifies other neighboring (i.e. within communication range)communication stations of its own existence, and also notifies thenetwork configuration. A communication station transmits a beacon at thehead of a transmission frame cycle, so the transmission frame cycle isdefined by the beacon interval. Also, each communication stationperforms a scanning operation on the channel for a period equivalent tothe transmission frame cycle, thereby discovering beacon signalstransmitted from nearby stations, and analyzes the information describedin the beacons to find out the network configuration (or to participatein the network). Each of the communication stations notify each other ofthe transmission/reception timing within each others transmission framecycle by exchanging beacon signals, thereby realizing loosetime-division multiple-access while performing random access to themedia in an autonomously dispersed manner according to CSMA procedures.

FIG. 1 illustrates a placement example of communication devicesconfiguring the wireless communication system according to oneembodiment of the present invention. With this wireless communicationsystem, no particular communication station is provided, with eachcommunication station operating in an autonomously dispersed manner,thereby forming an ad-hoc network. The drawing illustrates the say inwhich communication device #0 through communication device #6 aredistributed in the same space.

Also, the drawing illustrates the communication range of each of thecommunication devices with dotted lines, defining ranges wherein notonly can a communication device communicate with other communicationdevices in that range, but signals transmitted therefrom causeinterference therein. That is to say, the communication device #0 is ina range capable of communication with the neighboring communicationdevice #1 and communication device #4, the communication device #1 is ina range capable of communication with the neighboring communicationdevices #0, #2, and #4, the communication device #2 is in a rangecapable of communication with the neighboring communication devices #1,#3, and #6, the communication device #3 is in a range capable ofcommunication with the neighboring communication device #2, thecommunication device #4 is in a range capable of communication with theneighboring communication devices #0, #1, and #5, the communicationdevice #5 is in a range capable of communication with the neighboringcommunication device #4, and the communication device #6 is in a rangecapable of communication with the neighboring communication device #2.

In the event of performing communication between certain communicationdevices, there are communication device which can be heard from onecommunication device which is the other part of communication, butcannot be heard from the other communication device, i.e., “hiddenterminals”.

FIG. 2 schematically illustrates the functional configuration of awireless communication device operating as a wireless station in awireless network according to an embodiment of the present invention.The wireless communication device shown in the drawing can configure anetwork while avoiding collision by performing effective channel accesswithin the same wireless system in an autonomously dispersedcommunication embodiment with no control station disposed.

As shown in the drawing, the wireless communication device 100 isconfigured of an interface 101, a data buffer 102, a central controlunit 103, a beacon generating unit 104, a wireless transmission unit106, a timing control unit 107, an antenna 109, a wireless receptionunit 110, a beacon analyzing unit 112, and an information storage unit113.

The interface 101 exchanges various types of information with externalequipment (e.g., a personal computer (not shown) or the like) connectedto the wireless communication device 100.

The data buffer 102 is used to temporarily store data sent from devicesconnected via the interface 101, an data received over the wirelesstransmission path, before being sent via the interface 101.

The central control unit 103 centrally performs management of the seriesof information transmission and reception at the wireless communicationdevice 100, and access control of the transmission path. Operationcontrol such as collision avoidance processing at the like at the timeof beacon collision, for example, is performed at the central controlunit 103. Processing means for avoiding collision include moving thebeacon transmission position of the local station, stopping beacontransmission from the local station, requesting other stations to changethe beacon transmission position (to move the beacon transmissionposition or to stop), but the details of these processing procedureswill be described later.

The beacon generating unit 104 generates beacon signals periodicallyexchanged between neighboring wireless communication devices. In orderfor the wireless communication device 100 to operate a wireless network,the beacon transmission station of the local station and the beaconreception position from nearby stations and so forth are stipulated.This information is stored in the information storage unit 113, and alsois described in beacon signal and notified to the nearby wirelesscommunication devices. The configuration of beacon signals will bedescribed later. The wireless communication device 100 transmits beaconsat the head of transmission frame cycles, so the transmission framecycle at the channel which the wireless communication device 100 uses isdefined by beacon intervals.

The wireless transmission unit 106 performs predetermined modulationprocessing for wireless transmission of data temporarily stored in thedata buffer 102 and of beacon signals. Also, the wireless reception unit110 performs signal reception processing of information and beacons andthe like sent from other wireless communication devices at apredetermined time.

As for the wireless transmission/reception method at the wirelesstransmission unit 106 and the wireless reception unit 110, various typesof communication methods suitable for relatively close-distancecommunication, that can be applied to a wireless LAN, for example, canbe applied. Specifically, the UWB (Ultra Wide Band) method, OFDM(Orthogonal Frequency Division Multiplexing) method, CDMA (Code DivisionMultiple Access) method, and so forth, can be applied.

The antenna 109 performs wireless transmission of signals to anotherwireless communication device on a predetermined frequency channel, andcollects signals transmitted from other wireless communication device.With the present embodiment, a single antenna is provided, andtransmission and reception are not executable in parallel.

The timing control unit 107 performs timing control for transmission andreception of the wireless signals. For example, the beacon transmissiontiming form the local station at the head of the transmission framecycle, beacon reception timing from other wireless communicationdevices, data transmission/reception timing with other communicationdevice, and scanning operation cycle, and so forth, are controlled.

The beacon analyzing unit 112 analyzes beacon signals received fromneighboring stations, and analyzes the existence and so forth of theneighboring wireless communication devices. For example, informationsuch as the beacon reception timing of neighboring stations andneighboring beacon reception timing and so forth are stored in theinformation storage unit 113 as neighboring device information.

The information storage unit 113 stores execution procedure commands(programs describing collision avoidance processing procedures and soforth) for the series of access control operations executed at thecentral control unit 103, neighboring device information obtained as theresults of analyzing received beacons, and so forth.

With the autonomously dispersed type network according to the presentembodiment, each communication station notifies beacon information atpredetermined time intervals on a predetermine channel, therebynotifying other neighboring (i.e., within communication range)communication stations of own existence, and notify the networkconfiguration. The beacon transmission cycle is defined as a super framehere, and is 80 milliseconds, for example.

A communication station newly participating detects that it haspenetrated a communication range while listening to beacon signals fromnearby station by performing scanning operations, and also can know thenetwork configuration by analyzing the information described in thebeacons. The beacon transmission timing of the local station is then setto a timing at which no beacons are transmitted from nearby stations,while loosely synchronizing with the beacon reception timing.

Now, the beacon transmission procedures for each communication stationaccording to the present embodiment will be described with reference toFIG. 3.

Each communication station loosely synchronizes while listening tobeacons emitted nearby. In the event that a new communication stationemerges, the new communication station sets its own beacon transmissiontiming so as to not collide with the beacon transmission timing ofalready-existing communication stations.

In the event that there are no communication stations nearby, thecommunication station 01 can start transmitting beacons at an arbitrarytiming. The beacon transmission interval is 80 milliseconds (describedabove). In the example shown at the top tier in FIG. 3, B01 is a beacontransmitted from the communication station 01.

Hereafter, communication stations newly participating in thecommunication range set their own beacon transmission timings so as tonot collide with the already-existing beacon placement. At this time,each communication station acquires a preferential usage region (TPP)immediately following beacon transmission (described later), so it ismore preferably that the beacon transmission timing of the communicationdevices be uniformly scattered through the transmission frame cycle,rather than being concentrated, from the perspective of transmissionefficiency. Accordingly, with the present embodiment, the beacontransmission is started at approximately the center of the longest timespan of the beacon interval within the basic hearing range of the localstation.

For example, let us say that a new communication station 02 appears on achannel where only the communication station 01 exists, as shown at thetop tier in FIG. 3. At this time, the communication station 02 receivesbeacons from the communication station 01 so as to recognize theexistence thereof and the beacon position, sets its own beacontransmission timing at approximately the center of the beacon intervalof the communication station 01 as shown in the second tier in FIG. 3,and starts beacon transmission.

Further, let us say that a new communication station 03 appears. At thistime, the communication station 03 receives at least one of the beaconstransmitted from the communication station 01 and the communicationstation 02, and recognizes the presence of these already-existingcommunication stations. Then, as shown in the third tier in FIG. 3,transmission is started at a timing at approximately the center of thebacon intervals transmitted from the communication station 01 and thecommunication station 02.

Hereafter, each time a neighboring communication station newlyparticipates following the same algorithm, the beacon interval narrows.For example, as shown in the lowest tier in FIG. 3, the communicationstation 04 which appears next sets the beacon transmission timing at atiming at approximately the center of the bacon intervals set by thecommunication station 02 and the communication station 01, and moreover,the communication station 05 which appears next sets the beacontransmission timing at a timing at approximately the center of the baconintervals set by the communication station 02 and the communicationstation 04.

Note that there is also a usage method wherein the beacon transmissiontimings of each of the communication stations are placed in aconcentrated manner, and the reception operations are stopped for theremainder of the super frame cycle, so as to reduce electric powerconsumption of the device. In this case, processing for concentratingthe beacon transmission timings and so forth is performed between thecommunication stations performing communication, and beacons areconcentrated at one place or multiple places within the super framecycle, and transmitted.

Or, an arrangement may be made wherein the beacon transmission timing isset in accordance with a data transmission capacity unique to thecommunication station. In this case, communication stations with a greatamount of transmission data can set the beacon transmission timing to apoint-in-time such that the interval to the next beacon is long, andcommunication stations with little transmission data set the beacontransmission timing to a point-in-time such that the interval to thenext beacon is short.

However, in order to prevent beacons from saturating the band(transmission frame cycle), a smallest beacon interval B_(min) isstipulated, and placement of two or more beacon transmission timingswithin the B_(min) is not permitted. For example, in a case wherein theminimum beacon interval B_(min) is stipulated to 5 milliseconds in an80-millisecond transmission frame cycle, only 16 communication stationscan be contained in a range wherein airwaves reach.

FIG. 4 illustrates a configuration example of beacon transmission timingwhich can be placed within a super frame. Note that with the exampleshown in the drawing, the transition of time within the 80-millisecondsuper frame is represented as a clock where a needle moves on a circuitin the clockwise direction.

With the example shown in FIG. 4, a total of 16 positions 0 through Ffrom 0 to F are configured as “slots” as points-in-time where beacontransmission can be performed, i.3., where beacon transmission timingscan be placed. As described with reference to FIG. 3, beacon placementis performed following the algorithm wherein the beacon transmissiontiming of newly-participating stations are sequentially set atapproximately the center timing of beacon intervals set byalready-existing communication stations. In the event that B_(min) isstipulated to 5 milliseconds, only up to 16 beacons can be placed in asingle super frame. That is to say, no more than 16 communicationstations can participate in the network.

Now, though not shown in FIG. 3 and FIG. 4, each beacon is transmittedat a point-in-time having a slight intentional time offset from the TBTT(Target Beacon Transmission Time) which is the transmissionpoint-in-time of each beacon. This is referred to as “TBTT offset”. Withthe present embodiment, the TBTT offset value is determined by apseudo-random number. This pseudo-random number is determined by auniquely defined pseudo random sequence TOIS (TBTT Offset IndicationSequence), with the TOIS being updated each super frame cycle.

Due to setting the TBTT offset, even in a case wherein two communicationstations have placed the beacon transmission timing at the same slot inthe super frame, the actual beacon transmission point-in-time can beshifted, so even though the beacons may collide in one super framecycle, the communication stations can listen to each others beacons (ora neighboring communication station listen to both beacons) in anothersuper frame cycle, so the communication stations can recognize thattheir beacons have collided. The communication stations include the TOISto be set for each super frame cycle in the beacon information, andnotify the nearby stations (to be described later).

Also, with the present embodiment, even in a case that the communicationstations are in a power saving state wherein the electric power for thetransmitting/receiving devices is to be turned off when datatransmission/reception is unnecessary, and transmission/reception is notbeing performed, each communication station is required to performreception operations for a predetermined period before and followingtransmission of signals from the local station, i.e., to performcommunication operations for detecting collision called “Listen BeforeSend”, “Listen After Send”. Transmission signals as used here includeboth normal data frame transmission and beacon transmission.

Also, even in the case of not performing data transmission/reception,the communication stations are required to perform scanning operationsby consecutively operating the receiving device over one super frameonce every several seconds, to confirm whether there is no change in thepresence of nearby beacons and whether there is no shifting on the TBTTof the nearby stations. Note that this scanning operation may beperformed for detecting abnormal situations such as cases whereindetection is made that beacons or preferential transmission periods arecolliding, communication is cut off during a certain preferentialtransmission period, and so forth (to be described later).

For the scanning operation, basically a full scan is performed whereinthe reception device is operated consecutively throughout one superframe, but not necessarily restricted to this. For example a partialscan may be performed wherein the reception device is operated onlywithin a “time span wherein a beacon is transmitted” which thecommunication station recognizes. With the present embodiment whereinbeacon transmission timing placement is performed such as shown in FIG.4, the time span wherein a beacon is transmitted means before/after orimmediately after each TBTT, but is not restricted to this in the otherembodiments.

Shifting in TBTT can be confirmed by receiving beacons of other stationsand so forth. With the present embodiment, that stipulating within−B_(min)/2 milliseconds from the TBTT group recognized by the localstation as TBTT is defined as being “fast”, and that stipulating within+B_(min)/2 milliseconds as TBTT is defined as being “slow”. Thecommunication station corrects the point-in-time so as to match theslowest TBTT. Note however, that so long as the same rule is stipulatedthroughout the system, the point-in-time may be corrected so as to matchthe fastest TBTT. Thus, by all communication stations within the systemsetting the point-in-time to match the slowest (or fastest) TBTT, thecorrected point-in-time is propagated over the network. Consequently,even communication stations which cannot directly communicate can sharethe same reference point-in-time.

B. Transmission Prioritized Period TPP

Though the communication stations transmit beacons a constant intervals,a station which has transmitted the beacon is provided preferentialrights to transmission for a certain amount of time (e.g., 480microseconds) following transmitting the beacon. FIG. 5 illustrates theway in which preferential rights are provided to a beacon transmittingstation. With the present specification, this preferential section isdefined as a Transmission Prioritized Period (TPP). Also, the remainingsection of the super frame following the TPP is defined as a FairlyAccess Period (FAP), and communication is performed by normal CSMA/CAbetween the communication stations during this period.

FIG. 6 illustrates the configuration of a super frame. As shown in thedrawing, following beacon transmission from each communication station,a TPP is appropriated for the communication station which hastransmitted that beacon, and following the duration of the TPP a FAPstarts, with the FP ending at the beacon transmission from the nextcommunication station.

Each communication station is permitted transmission in intervals ofSIFS with regard to beacon and packet transmission within the TPP of thelocal station, and is permitted DIFS+backoff transmission for otherpackets. That is to say, each time a beacon is transmitted, anopportunity for preferentially transmitting data is obtained.

Also, while each communication basically transmits one beacon for eachsuper frame cycle, in some cases, a communication station is permittedto transmit multiple beacons or beacon-like signals, and a TPP can beacquired each time these beacons are transmitted. In other words, acommunication station can secure preferential transmission resources inaccordance with the number of beacons transmitted per super frame. Now,a beacon which a communication station always transmits at the head of asuper frame cycle will be called a “normal beacon”, and the second andsubsequent beacons transmitted at other timings or acquiring TPPs orother objects will be called “auxiliary beacons”.

FIG. 29 illustrates the operations for a communication station to starttransmission each of a TPP section and FAP section.

In a TPP section, following transmitting a beacon from the localstation, a communication station can start transmission following ashorter bucket interval SIFS. In the example shown in the drawing, anRTS packet is transmitted from the beacon transmission station followingthe SIFS. The subsequently transmitted CTS, data, and ACK packets arealso transmitted in SIFS frame intervals in the same way, so the seriesof communication procedures cannot executed without interruption fromneighboring stations.

Conversely, with a FAP section, the beacon transmission station startstransmission after standing by for a LIFS+random backoff, the same aswith other nearby stations. In other words, all communication stationsare uniformly provided with transmission rights by random backoffs. Inthe example shown in the drawing, following another station havingtransmitting a beacon, first, the media station is monitored for theduration of a DIFS, and in the event that the media is clear during thistime, i.e., in the event that there are not transmission signals, arandom backoff is performed, and further in the event that there are nosignals transmitted during this time, a RTS packet is transmitted. Notethat the series of packets of CTS, data, ACK, etc., transmitted owing toRTS signals, are transmitted at SIFS frame intervals, thereby allowingthe series of transactions to be executed without being interrupted byneighboring stations.

According to the traffic management method of signals described above,transmission rights can be preferentially obtained by communicationstations with higher order of preference setting shorter frameintervals.

However, the basic increment of a Transmission Prioritized Period TPP isfixed to a constant period equal to or smaller than the smallest beaconinterval, and following this, transition is made to FAP, which is aperiod wherein all communication stations obtain communication rightsunder uniform conditions of common IFS and random backoff. Accordingly,in the event that a communication station needs a communication bandexceeding the Transmission Prioritized Period TPP obtainable by onebeacon transmission per super frame due to a request from the upperlayer, the communication station can transmit auxiliary beacons besidesthe normal beacon for example, to further acquire TPPs. Note that in theevent that the object is to secure band, consecutive arraying ofTransmission Prioritized Periods TPPs is also permissible. In this case,TPPs can continue for a period exceeding the smallest beacon interval.

FIG. 30 illustrates the way in which a communication station transmitsmultiple virtual beacons called auxiliary beacons to increase theTransmission Prioritized Period. In the example shown in the drawings,the communication station #1 discovers a beacon slot open in the superframe and places its own auxiliary beacon there, thereby obtainingmultiple TPPs in one super frame, in order to secure the communicationband requested from the upper layer. Note that as described above, inFIG. 30 there are cases wherein the existing FAP is eliminated duringthe TPP of the communication station #1 with regard to sections whereinthe communication station #1 has secured continuous TPPs, thereby usingthis a consecutive TPPs. In a system wherein a super frame is configuredin an autonomously dispersed manner by exchange of NBOI information, anavailable beacon slot can be searched taking into consideration thehidden terminal problem, so the method for obtaining band usingauxiliary beacons is simple.

FIG. 31 is a state transmission diagram of a wireless communicationdevice operating as a communication station in the present embodiment.In the example of the drawing, two states are defined; the “preferentialtransmission mode”, equivalent to a TPP period wherein the local stationhas acquired preferential transmission rights, and the “normaltransmission mode”, equivalent to a FAP period wherein no local stationhas acquired preferential transmission rights.

Under the normal operation mode, the communication station startstransmission following standing by for PIFS+a random backoff.

Now, following the beacon transmission timing TBTT of the local stationarriving and transmitting the beacon, the mode makes transition to thepreferential transmission mode, whereby a Transmission PrioritizedPeriod TPP is obtained.

In the preferential transmission mode, transmission rights can beacquired without interruption from neighboring stations, by transmittingin SIFS frame intervals.

The communication station continues in the preferential transmissionmode for a Transmission Prioritized Period TPP of a length equivalent tothe band amount required from the upper layer.

Then, upon the TPP ending and going to FAP, or upon receiving a beaconfrom another station, the mode returns from the preferentialtransmission mode to the normal operation mode.

Also, FIG. 32 illustrates another example of the state transmissiondiagram of a wireless communication device operating as a communicationstation. In the example of the drawing, in addition to the “preferentialtransmission mode”, equivalent to a TPP period wherein the local stationhas acquired preferential transmission rights, and the “normaltransmission mode”, equivalent to a FAP period wherein no local stationhas acquired preferential transmission rights, a “preferentialtransmission mode”, equivalent to a Transmission Prioritized Period TPPof another station, is defined.

Under the normal operation mode, the communication station startstransmission following standing by for a normal frame period of PIFSplus a random backoff. During the FAP period, all communication stationswithin the system transmit according to PIFS+backoff.

Now, following the beacon transmission timing TBTT of the local stationarriving and transmitting the beacon, the mode makes transition to thepreferential transmission mode, whereby a Transmission PrioritizedPeriod TPP is obtained.

In the preferential transmission mode, transmission rights can beacquired without interruption from neighboring stations, by transmittingwith standby periods of SIFS which is frame intervals shorter than PIFS.The communication station continues in the preferential transmissionmode for a Transmission Prioritized Period TPP of a length equivalent tothe band amount required from the upper layer. Then, upon the TPP endingand going to FAP, the mode returns from the preferential transmissionmode to the normal operation mode.

Also, upon receiving a beacon from another station and entering thepreferential transmission period of that station, the mode makestransition to a non-preferential transmission mode. In thenon-preferential transmission mode, transmission is started followingstanding by for a period wherein a random backoff is added to DIFS whichis a frame interval even longer than the PIFS frame interval in thenormal transmission mode.

Upon the TPP of the other station ending and making transition to FAP,the mode returns to the normal transition mode.

Note that while an example has been described above wherein acommunication station consecutively attempts transmission in DIFS frameintervals during TPP periods of nearby stations as well, there are caseswherein no transmission is attempted during TPP periods of otherstations, and the communication station goes into a power saving stateby turning off the power or the like. Also, rather than consecutivelyattempting transmission in DIFS frame intervals, examples of applicationinclude attempting transmission following confirmation of the TPP beingreleased by other means.

While normal beacons are transmitted for network configuration,auxiliary beacons are transmitted in order to acquire TransmissionPrioritized Periods TPPs, so there is no need for all informationincluded in a normal beacon (described later) to be described in anauxiliary beacon. Accordingly, there are cases wherein only informationrelating to TPP acquisition is included in the auxiliary beacon. In anextreme example, an auxiliary beacon can be configured of one bit (oraround several bits) of information to the effect that the signal isbeing transmitted upon acquisition of a TPP.

Also, in an autonomously dispersed communication system, a framework forrealizing Transmission Prioritized Period TPP acquisition bycommunication stations can be realized even without using auxiliarybeacons. With a system wherein auxiliary beacons are not used, networkoperations (collusion avoiding operations) the same as those of a caseof using auxiliary beacons to notify that a Transmission PrioritizedPeriod TPP has been acquired can be realized by describing, in a part ofthe signals transmitted upon the communication station having obtained aTransmission Prioritized Period TPP, a message to the effect that thesignals are being transmitted using a Transmission Prioritized PeriodTPP. The details of this point will be described later. Thecommunication stations notify each other of the reception/transmissiontiming of each other within the super frame, based on beacon signalnotification or description in a part of the signals such as the dataframe, and randomly access the media by CSMA procedures in anautonomously dispersed manner, while realizing loose time-divisionmultiple access.

While an example has been illustrated here wherein the beacontransmitting station starts the TPP immediately following beacontransmission, there is no need to be restricted to this, and anarrangement may be made wherein a TPP starting point-in-time is set at arelative position (point-in-time) from the beacon transmissionpoint-in-time, for example.

Also, while description has been made in the above description thatpreferential transmission rights are provided only to the communicationstation during TPP, but the communication station called up by thecommunication station during TPP is also provided with a TransmissionPrioritized Period TPP. Basically, transmission is given preference withTPP, but in the event that it is known that the local communicationstation has nothing to transmit but another station has informationwhich it wants to transmit to the local station, a paging message or apolling message may be sent to the “other station”.

On the other hand, in the case that the local station has transmitted abeacon but has nothing to transmit and does not know whether otherstations have information to be transmitted to the local station, thiscommunication station does not perform communication operations,relinquishes the preferential transmission rights granted by the TPP,and transmits nothing. As a result, another station start transmissionin this TPP time span, following elapsing of a DIFS+backoff orPIFS+backoff.

Taking into consideration the fact that TPPs immediately followtransmission of beacons as shown in FIG. 6, an arrangement is morepreferable wherein the beacon transmission timings of the communicationstations are scattered uniformly throughout the transmission frame cyclerather than an arrangement wherein the beacon transmission timings areconcentrated, from the perspective of transmission efficiency.Accordingly, with the present embodiment, beacon transmission isbasically started at approximately the center of the longest time spanof beacon intervals in the range that can be heard by itself. Of course,there is also a usage method wherein the beacon transmission timings ofthe communication stations are placed in a concentrated manner and thereception operations are stopped in the remaining transmission framecycle, so as to reduce the power consumption of the devices.

In the behavior at the time of collision in the wireless networkaccording to the present embodiment, generally the same principle can beapplied for beacon collision avoidance operations with regard tocollision of normal beacons one with another, collision of normalbeacons and auxiliary beacons, and collision of auxiliary beacons onewith another. Moreover, signals periodically transmitted each superframe (data frames and so forth) by acquiring Transmission PrioritizedPeriods TPPs can also be handled in the same way as beacons with regardto collision detection and collision avoidance operations, due to thenature of being transmitted and received in super frame intervals. Forexample, the same advantages can be obtained with regard to processingof collision of Transmission Prioritized Periods with no auxiliarybeacon transmission as well, by collision detection and collisionavoidance procedures the same as with the case of beacons. Accordingly,in the following, collision of auxiliary beacons and TransmissionPrioritized Periods TPPs, in addition to normal beacons, will bedescribed as beacon collision, for the sake of ease of description.

C. Frame Format of Beacon

FIG. 7 illustrates an example of the format of a beacon frametransmitted with the autonomously dispersed wireless communicationsystem according to the present embodiment.

With the example in the drawing, a beacon includes a TA (TransmitterAddress) field, which is an address, uniquely indicating the originatingstation, a Type field indicating the type of the beacon, a NBOI/NBAI(Neighboring Beacon Offset Information/Neighboring Beacon ActivityInformation) field which is reception point-in-time information ofbeacons receivable from nearby stations, a TOIS (TBTT Offset IndicationSequence) field which is information indicating the TBTT offset value(Described above) in the super frame cycle in which the beacon has beentransmitted, an ALERT field for storing TBTT changes and other sorts ofinformation which should be passed on, a T×Num field which indicates theamount of resources which the communication device has securedpreferentially, and a Serial field indicating an exclusive and uniqueserial No. assigned to the beacon in a case of transmitting multiplebeacons within the super frame cycle.

In the Type field is described the type of the beacon in an 8-bit lengthbitmap format. With the present embodiment, whether the beacon is a“normal beacon” which the communication station transmits just once atthe head of each super frame or an “auxiliary beacon” transmitted forobtaining preferential transmission rights, is indicated with valuesfrom 0 through 255 indicating priority, as information for identifyingwhich the beacon is. Specifically, in the case of a normal beacon, whichmust be transmitted once every super frame, 255 indicating the greatestpriority is assigned, and for auxiliary beacons, one of the values of 0through 254 which is equivalent to the priority of the traffic, isassigned.

With a system wherein auxiliary beacons are not used, the Type field canbe described in a part of the signals, to indicate the priority ofreservation or preferential usage of signals (data frame or the like)periodically transmitted, in which the reserved usage period or apreferential usage period TPP is set.

The NBOI field is information describing the position (receptionpoint-in-time) of beacons of nearby stations which the local station iscapable of receiving in the super frame. With the present embodiment,information relating to the placement of the received beacon isdescribed in a 16-bit length bitmap format, since a maximum of 16 slotsfor placing beacons are provided within a super frame, as shown in FIG.4. That is to say, the normal beacon transmission point-in-time ismapped to the head bit (MSB) of the NBOI field as a reference, thepositions (reception points-in-time) of beacons which the local stationis capable of receiving are mapped to bits at relative positions fromthe normal beacon transmission point-in-time of the local station, 1 iswritten to bits corresponding to the normal and auxiliary beaconrelative position (offset) and relative position (offset) of receivablebeacons, and the bit positions corresponding to other relative positionsare left at 0.

For example, under a communication environment wherein a maximum of 16communication stations 0 through F are contained as shown in FIG. 4, inthe event that a communication station 0 creates an NBOI field of“1100,0000,0100,0000”, this indicates that “beacons of communicationstation 1 and communication station 9 are receivable”. That is to say, 1is marked in the event that a beacon is receivable with regard to a bitcorresponding to the relative position of a receivable beacon, and 0,i.e., a space, is assigned in the case that this is not received. Also,the reason that the MSB is 1 is that the local station transmitsbeacons, and 1 is also marked at the position matching the point-in-timeof the local station transmitting auxiliary beacons as well.

Also, while the description above has been made assuming that the NBOIfield is transmitted and received in a bitmap format corresponding tothe point-in-time in the super frame, configuring the NBOI field in abitmap format is not necessarily indispensable, and the object of thepresent invention can be achieved with an arrangement wherein this isconfigured of an information group indicating which time span in thesuper frame is used for communication, and is ultimately transmitted andreceived in a format such that the above-described processing can beperformed.

Also, while description above has been made that the relative positions(points-in-time) of the transmitted and received beacons are marked, thepoint-in-time of the preferential transmission period can also be markedin the NBOI as a matter of course, whereby, in addition to detection ofbeacons one with another, collision of signals which are periodicallytransmitted using the Transmission Prioritized Period TPP with beacons,and collision of signals which are periodically transmitted one withanother, can also be detected.

Also, the NBAI field is for reducing hidden terminals with regard tobeacon reception; the NBAI field is set in the frame format of thebeacon, and information identifying “beacons which the local stationactually performs reception processing for” is described in the sameformat as the NBOI field. The NBAI field has bits placed based on thetransmission point-in-time of the normal beacon of the local station inthe same format as with the NBOI field, and information for identifyingthe TBTT which the local station actual performs reception processingfor is described in bitmap format.

The communication stations do not receive beacons of other stations inthe sleep mode state. Accordingly, in the sleep mode state, beacons aretransmitted in the state that all zeroes are set to the NBAI bits(except for the point-in-time of the local station performing beacontransmission). On the other hand, upon the communication stationentering a communication state with another station, operations forreceiving normal beacons of the nearby stations are performed. In thiscase, beacons are transmitted in the state of ones set to the NBAI bitscorresponding to the reception points-in-time (TBTT) of the normalbeacons of the nearby stations.

In the event that a nearby station is transmitting an auxiliary beacon,1 is set to the NABI bit corresponding to the reception point-in-time(TBTT) of the auxiliary beacon received, only in the event that thepreferential transmission with the auxiliary beacon is determined to bemade to the local station. Whether the preferential transmission withthe auxiliary beacon is being made to the local station or not isdetermined based on whether or not a communication state has beenestablished with the communication station transmitting the auxiliarybeacon.

Further, in the event that the recipient of data transmitted in the TPPaccessory to the auxiliary beacon for each auxiliary beacon is specifiedby some sort of means, the NBAI bit corresponding to the receptionpoint-in-time (TBTT) of the auxiliary beacon is set to 1 only for anauxiliary beacon wherein the recipient of the data is determined to bethe local station. That is to say, the communication station determineswhether or not to set the NBAI bit to 1, according to whether or not theauxiliary beacon transmitted on the time span and the signal transmittedby the other station using TPP are transmitted to the local station(i.e., whether or not the local station needs to receive the signals).

On the other hand, the station which has received the beacon obtains anOR of the NBAI bits in the received beacon by shifting according to thebeacon reception point-in-time according to the same procedures forcompiling the Rx NBOI Table (described above), and determines whether ornot to perform transmission forbidden processing in each TBTT set in thesuper frame.

In the event that the OR of the NBAI bit is 1, the communication stationsets from the TBTT point-in-time or a point-in-time slightly prior tothat through a certain period stipulated by the maximum length of TBTToffset+beacon length to a transmission forbidden state, so as to notobstruct beacon reception of other stations. However, in the event thatthe TBTT is the beacon transmission point-in-time of the local station,transmission forbidden processing is not performed, and the frameincluding beacon information is transmitted.

The TOIS field stores a pseudo-random sequence for determining theabove-described TBTT offset, and indicates how much of a TBTT offset thebeacon is being transmitted with. Providing a TBTT offset enables actualbeacon transmission point-in-time to be shifted even in the event thattwo communication stations set beacon transmission timings to the sameslot in a super frame, so even though the beacons may collide in onesuper frame cycle, the communication stations can listen to each othersbeacons (or a neighboring communication station listen to both beacons)in another super frame cycle, so the communication stations canrecognize that their beacons have collided.

FIG. 8 shown the TBTT and actual beacon transmission point-in-time. Asshown in the drawing, in the event that the TBTT offset is defined asbeing one point-in-time of TBTT, TBTT+20 microseconds, TBTT+40microseconds, TBTT+60 microseconds, TBTT+80 microseconds, TBTT+100microseconds, and TBTT+120 microseconds, which TBTT offset will be usedfor transmission is determined each super frame cycle, and the TOIS isupdated.

Also, in the event that transmission cannot be performed at thepoint-in-time that the communication station intended, due to detectionof collision with signals form another station or the like, all zeroesor the like are stored to the TOIS, and transmission is made to nearbystations capable of receiving beacons to the effect that the beacontransmission timing this time could not be performed at the intendedpoint-in-time. Specific usage forms of the TOIS field will be describedlater.

The ALERT field stores information to be transmitted to nearby stationsin an abnormal state. For example, in the event that there are plans tochange the normal beacon TBTT to avoid beacon collision or the like, orin the event of requesting stopping of auxiliary beacon transmission toa nearby station, a description is made in the ALERT field to thateffect. Specific usage forms of the ALERT field will be described later.

The number of auxiliary beacons which the station is transmitting in thesuper frame cycle is described in the T×Num field. Since thecommunication station is given a TPP, i.e., preferential transmissionrights, following beacon transmission, the number of auxiliary beaconswithin the super frame cycle is equivalent to the percentage of timewherein resources are preferentially secured and transmission isperformed.

The serial No. assigned to the beacon in a case of transmitting multiplebeacons within the super frame is written to the Serial field. Anexclusive and unique number is described for each of the beaconstransmitted within the super frame, as serial Nos. of beacons. With thepresent embodiment, relative point-in-time information indicating whatnumber in order TBTT the auxiliary beacon is being transmitted at, basedon the normal beacon of the local station, is described in the Serialfield as the serial No.

While normal beacons are transmitted for network configuration,auxiliary beacons are transmitted in order to acquire TransmissionPrioritized Periods TPPs, so there is no need for all informationincluded in a normal beacon (described later) to be described in anauxiliary beacon. Accordingly, there are cases wherein only informationrelating to TPP acquisition is included in the auxiliary beacon.

Also, with a system wherein auxiliary beacons are not used, collision ofsignals which are periodically transmitted/received using theTransmission Prioritized Period TPP with beacons, and collision ofsignals which are periodically transmitted/received one with another,can be handled in the same way as with collisions of beacons one withanother, and periodically transmitted/received signals one with another,by describing, in a part of the signals transmitted upon thecommunication station having obtained a Transmission Prioritized PeriodTPP, information the same as that of the normal beacon.

For example, in the event of setting priority for TransmissionPrioritized Period TPP, there is the need to include the Type field inauxiliary beacons and signals transmitted periodically using theTransmission Prioritized Period as well.

Also, in the case of providing a random offset to the transmissiontiming of signals transmitted periodically using the TransmissionPrioritized Period TPP and in the case of employing a mechanism forchanging the transmission timing of periodically transmitted/receivedsignals to avoid collision, there is the need to include a TOIS field inauxiliary beacons and signals transmitted periodically using theTransmission Prioritized Period as well.

Also, in cases wherein the communication stations are to notify eachother of the relative point-in-time position of the transmission timingof signals transmitted periodically using the Transmission PrioritizedPeriod TPP as to the normal beacon (offset from the normal beacon), inorder to detect collision with a beacon, there is the need to include aSerial field in auxiliary beacons and signals transmitted periodicallyusing the Transmission Prioritized Period as well.

D. TBTT Settings for Normal Beacon

After turning on the electric power, a communication station firstperforms a scanning operation, i.e., attempts signal receptioncontinuing over the duration of a super frame or longer, and confirmsthe presence of beacons transmitted by nearby stations. In the eventthat no beacons are received from nearby stations in this process, thecommunication station sets an arbitrary timing as the TBTT timing. Onthe other hand, in the event of receiving a beacon transmitted fromnearby stations, the logical sum (OR) of the NBOI fields of the beaconsreceived from the nearby stations is taken and referred, and finally abeacon transmission timing is extracted from a timing equivalent to abit position which is not marked.

Basically, the communication station obtains the preferential usageperiod (TPP) immediately following transmission of beacon, so anarrangement is more preferable wherein the beacon transmission timingsof the communication stations are scattered uniformly throughout thesuper frame cycle, from the perspective of transmission efficiency.Accordingly, based on the results of the OR of the NBOIs obtained fromthe beacons received from the nearby stations, the center of the sectionwhere the run length of the space is the longest is determined as thebeacon transmission timing.

Now, in the event that the TBTT interval wherein the run length islongest, is smaller than the minimum TBTT interval (i.e., equal to orsmaller than B_(min)), new communication stations cannot participate inthis system.

Also, in another embodiment, there are cases wherein the beacontransmission point-in-time TBTT of the local station is set to anadjacent point-in-time, such as immediately following a beacon alreadytransmitted, according to communication attributes and so forth. In thiscase, processing is added such as taking into consideration ordering ofthe beacon transmission points-in-time among the communication stationswhich are to actually perform communication.

FIG. 9 illustrates the way in which the TBTT of a communication stationnewly participating is set based on the NBOIs of the beacons receivedfrom nearby stations. The example shown in the drawing is described fromthe perspective of a newly-appearing communication station A, with acommunication environment wherein nearby the communication station A area communication station 0, communication station 1, and communicationstation 2. Let us say that the communication station A is capable ofreceiving beacons from the three stations 0 through 2 within a superframe by performing a scanning operation.

The beacon reception points-in-time of the nearby stations are handledas relative positions to the normal beacon of the local station, whichis described in the NBOI field in bitmap format (described above). Atthe communication station A, the NBOI fields of the three beaconsreceived from the nearby stations are shifted according to the receptionpoint-in-time of the beacons so as to match the corresponding bitposition on the time axis, and the OR is obtained of the NBOI bits foreach timing, thereby integrating the NBOIs for reference.

The sequence obtained as a result of integrating and referencing theNBOI files of the nearby stations is “1101,0001,0100,1000” indicated by“OR of NBOIs” in FIG. 9. 1 indicates the relative position of a timingregarding which a TBTT has already been set in the super frame, and 0indicates the relative position of a timing regarding which a TBTT notyet been set. In this sequence, the place where the spaces (zeroes) formthe longest run length is a candidate for placing a new beacon. With theexample shown in FIG. 9, the longest run length is 3, so there are twocandidates. The communication station A has set of these the 15th bit asthe normal beacon TBTT for itself.

The communication station A sets the point-in-time of the 15th bit asthe normal beacon TBTT for itself (i.e., head of the super frame foritself), and starts beacon transmission. At this time, the NBOI fieldwhich the communication station A transmits lists the receptionpoints-in-time of the beacons of the communication stations 0 through 2from which beacon reception can be made in a bitmap format wherein bitpositions equivalent to relative positions from the transmissionpoint-in-time of the normal beacon of the local station are marked. Thisis as indicated by “NBOI for TX (1 Beacon TX)” in FIG. 9.

At the time of the communication station A obtaining preferentialtransmission rights by transmission of an auxiliary beacon or the like,the longest run length of spaces (zeroes) in the sequence indicated by“OR of NBOI” obtained by integrating the NBOI fields of the nearbystations is then further searched, and the transmission point-in-time ofthe auxiliary beacon (Transmission Prioritized Period) is set to theplace of the spaces that has been found. In the example shown in FIG. 9,a case is assumed for transmitting two auxiliary beacons (i.e.,acquiring two Transmission Prioritized Periods), and the auxiliarybeacon transmission timings (setting timings for TransmissionPrioritized Periods) are set to the points-in-time of the 6th bit and11th bit of the “OR of NBOIs”. In this case, the NBOI field which thecommunication station A transmits is further marked at the place wherethe local station performs auxiliary beacon transmission (relativeposition to the normal beacon) in addition to the normal beacon of thelocal station and the relative positions of the beacons received fromthe nearby stations, as shown in NBOI for TX (3 Beacon TX)”.

In the event of the communication stations each setting their own beacontransmission timing TBTTs with the above-described processing proceduresand transmitting beacons, beacon collision can be avoided underconditions that the communication stations are stationary and that therange of reach of the airwaves does not change. Also, QoS communicationcan be provided wherein resources are preferentially allocated tocommunication between certain communication stations for a certain timespan, by setting Transmission Prioritized Periods by transmittingauxiliary beacons (or signals like multiple beacons) within the superframe according to the order of preference of the transmission data.Also, each communication station can autonomously know the degree ofsaturation of the system by referring the number of beacons (NBOI field)received from the nearby stations, so preferential traffic can becontained while taking into consideration the degree of saturation ofthe system at each communication station, even though the system isautonomously controlled. Further, the beacon transmission points-in-timeare placed so as to not collide, due to the communication stationsreferring to the NBOI files of the received beacons, so frequentcollision can be avoided even in cases wherein multiple communicationstations contain preferential traffic.

E. Beacon Collision Scenarios and Collision Avoidance Procedures

Under the conditions that the communication stations are stationary andthat the range of reach of the airwaves does not change, beaconcollision can be avoided (described above). Conversely, if the range ofreach of the airwaves changes due to the communication stations movingor the like, there will be cases wherein the beacons transmitted fromthe communication stations collide.

FIGS. 10A-10D illustrate the way in which beacons collide due to changein the range of reach of the airwaves. The drawings illustrate a casewherein systems configuring networks approach each other.

At FIG. 10A, communication stations the STA0 and the STA1 exist in arange where airwaves from communication stations the STA2 and the STA3cannot reach, with the STA0 and the STA1 performing communication. Also,the STA2 and the STA3 perform communication completely independent fromthese. In this case, the beacon transmission timings are set for eachcommunication station in a independent manner for each system, but asshown in FIG. 10B, beacon transmission timings which unfortunately matchhave been set between the stations which do not recognize each other.

Subsequently, upon (the range of reach of the airwaves of) thecommunication stations moving to where each of the communicationstations can transmit/receive, as shown in FIGS. 10C-10D, a situationoccurs in which the beacons of the stations collide.

In such a case, there is the need for at lease one of the stations whichhas caused the collision to change the beacon transmission point-in-timeto avoid collision. FIG. 11 shows an example of collision detection andTBTT changing procedures. The example shown here is a case wherein theTBTT of the beacon transmitted by the STA0 and the TBTT of the beacontransmitted by the STA2 have perfectly matched the point-in-time TBTT0.

At point-in-time T0, the beacon transmission TBTT for both the STA0 andthe STA2 arrives, so each transmit beacons at a point-in-time shiftedfrom the point-in-time T0 by a TBTT offset. At point-in-time T0, theTBTT offset of the STA0 and the TBTT offset of the STA2 happen to be thesame, so the beacons collide, and neither the STA0 nor the STA2 iscapable of detecting that the beacons are colliding. It should be notedthat the communication stations are not capable of activatingtransmission operations and reception operations simultaneously.

The next super frame comes, and the TBTT for both the STA0 and the STA2arrives at point-in-time T1, so beacon transmission processing isactivated again. Now, let us say that while the TBTT offset at the STA2is zero, the TBTT offset selected at the STA0 is a relatively largevalue. By shifting the actual beacon transmission point-in-time by TBTToffset, even though the beacons may collide in one super frame cycle,the communication stations can listen to the beacons of each other inanother super frame cycle.

In the example shown in the drawing, the STA0 operates the receivingdevice before and after beacon transmission, and accordingly canrecognize that the STA2 is transmitting beacons at a TBTT point-in-timeclose to that of itself. In the same way, the STA2 operates thereceiving device before and after beacon transmission, and accordinglycan recognize that the STA0 is transmitting beacons at a TBTTpoint-in-time close to that of itself. Whether or not a beacon has beenreceived close to the TBTT of it self is determined based on whether ornot a beacon has been received within the range of the local beaconTBTT±B_(min)/2.

Now, the STA0 determines to change its own TBTT, i.e., beacontransmission position, the reason being that a beacon of another stationhas been received immediately prior to transmission of its own beacon.On the other hand, at the STA2, a beacon of another station has beenreceived close to the TBTT point-in-time of its own beacon, but thebeacon was received following transmission of its own beacon, so no TBTTchange is performed.

Also, even in the event that the STA0 and the STA2 are not performingdata transmission/reception and are in a power saving state, both arerequired at the time of signal transmission to perform receptionoperations for a predetermined period before and following transmissionof signals from the local station, i.e., Listen Before Send and ListenAfter Send, and such reception operations enable the communicationstations to recognize the beacons of each other.

In the case of changing the beacon transmission position, the STA0 makesnotification to the nearby stations that it is going to change the TBTT,using the ALERT field of the beacon to be transmitted (the alert fieldis a field for storing information to be transmitted to the nearbystations in an abnormal situation). Further, the STA0 executes scanningfor at least one super frame, to collect information for determining thenew TBTT.

With the example shown in FIG. 11, the STA0 recognizes beacon collisionnear the point-in-time T1, and immediately activates TBTT changingprocessing, but this processing may be executed after a delay of one ortwo super frames, due to delay in processing within the communicationstation.

Upon the STA0 finding an available TBTT by the procedures described withreference to FIG. 9, the TBTT 1 is set as the new TBTT, and does notperform beacon transmission at point-in-time T2 but instead performsbeacon transmission at point-in-time T3 instead, and subsequentlyperforms beacon transmission at the timing of TBTT1 with a TBTT offset.

On the other hand, the STA2 transmits its beacon at point-in-time T2 asif nothing had happened, and subsequently continues to transmit itsbeacon at the timing of TBTT0 with a TBTT offset. With the example shownin FIG. 11, the STA2 does not change TBTT, but there are cases whereinthe STA2 performs scanning processing to know the state of the network,having recognized that the networks have crossed from reception of thebeacon of the STA0.

In the event that a communication station recognizes a beacon notifyingin the ALERT field that the TBTT is to be changed, or recognizes that nobeacon is being transmitted near the TBTT of beacons received so far, ascan is executed to tell where the new TBTT of the beacon has beendetermined at (not shown).

Also, an arrangement may be made wherein, at the time of reception of abeacon of another station immediately following the beacon transmissionpoint-in-time of the local station, a request is made to the originatorof the beacon received immediately following to change the beacontransmission point-in-time. FIG. 12 illustrates an example of TBTTchanging procedures wherein one station of colliding beacons sends abeacon transmission point-in-time changing request to the other station.

Upon the TBTT for both the STA0 and the STA2 arriving at point-in-timeT1, beacon transmission processing is activated for both. Now, let ussay that while the TBTT offset at the STA2 is zero, the TBTT offsetselected at the STA0 is a relatively large value. In this case, the STA0operates the receiving device before and after signal transmission suchas beacons, and accordingly can recognize that the STA2 is transmittingbeacons at a TBTT point-in-time close to that of itself. In the sameway, the STA2 operates the receiving device before and after beacontransmission, and accordingly can recognize that the STA0 istransmitting beacons at a TBTT point-in-time close to that of itself.

Now, the STA2 transmits a message to the STA0 “to the effect of you arerequested to change your TBTT”. The STA0 operates the receiving devicefor a certain while before and following signal transmission such as abeacon even in a power saving state (described above), and accordinglycan receive this message.

In response to having received a TBTT change request message, the STA0makes notification to the nearby stations to the effect that the TBTTwill be changed, using the ALERT field of the beacon transmitted.Further, the STA0 executes scanning for at least one super frame, tocollect information for determining the new TBTT.

Upon the STA0 finding an available TBTT by the procedures described withreference to FIG. 9, the TBTT 1 is set as the new TBTT, and does notperform beacon transmission at point-in-time T4 but instead performsbeacon transmission at point-in-time T5 instead, and subsequentlyperforms periodic beacon transmission at the timing of 0 with a TBTToffset.

On the other hand, the STA2 transmits its beacon at point-in-time T2 asif nothing had happened, and subsequently continues to transmit itsbeacon at the timing of TBTT0 with a TBTT offset. With the example shownin FIG. 12, the STA2 does not change TBTT, but there are cases whereinthe STA2 performs scanning processing to know the state of the network,having recognized that the networks have crossed from reception of thebeacon of the STA0.

Note that with the above-described processing, the rule is that at thetime of beacons colliding, a communication station which has received abeacon from another station immediately prior to its own beacontransmission point-in-time is to change its own beacon transmissionpoint-in-time, however, a reverse arrangement may be made wherein acommunication station which has received a beacon from another stationimmediately following its own beacon transmission point-in-time is tochange its own beacon transmission point-in-time.

Next, operations relating to a communication station detecting collisionof signals in an autonomously dispersed wireless network according tothe present embodiment will be described in further detail. FIG. 33through FIG. 37 illustrate several examples of collision detectingprocedures with regard to an example wherein beacons have collidedbetween communication stations which are transmitting and receivingdata. Following detection of collision, the already-described proceduresare used to activate the TBTT changing procedures as necessary.

FIG. 33 illustrates an example of a case wherein the beacon transmissionpoint-in-time have collided between the STA0 and the STA2, while theSTA0 is continuing to transmit data to the STA1.

Upon the TBTT for both the STA0 and the STA2 arriving at point-in-timeT0, beacon transmission processing is activated for both. Now, let ussay that the TBTT offset selected at the STA2 is a relatively largervalue that the TBTT offset of the STA0.

The STA0 transmits the beacon as planned (BO in the drawing). Since theSTA2 operates the receiving device before and after beacon signaltransmission, it can recognize that the STA0 is transmitting beacons ata TBTT point-in-time close to that of itself. Further, the STA2 followsCSMA/CA procedures to set a NAV while signals of other stations arepresent, and refrains from signal transmission. Consequently, even inthe event that there was a schedule to transmit a beacon atpoint-in-time T1, this is delayed.

The STA0 continues to transmit data to the STA1 (D0 in the drawing). Theduration to the point-in-time of receiving the ACK is written to theDuration field for the data for the purpose of virtual carrier sense,and the STA2 interprets this an refrains from transmitting signals untilthe point-in-time T2.

Subsequently, the STA2 makes transition to a signal transmittable statefollowing elapsing of PIFS (or SIFS)+a random delay amount frompoint-in-time T2, and transmits a beacon at point-in-time T3 (B2 in thedrawing).

Since the STA0 operates the receiving device before and after signaltransmission, it can recognize that the STA2 is transmitting beacons ata TBTT point-in-time close to that of itself.

The STA2 determines to change its own TBTT, i.e., beacon transmissionposition, the reason being that a beacon of another station has beenreceived immediately prior to transmission of its own beacon. On theother hand, at the STA0, a beacon has been received close to the TBTTpoint-in-time of its own, but the beacon was received followingtransmission of its own beacon, so no TBTT change is performed.

In the case of changing the beacon transmission position, the STA2 makesnotification to the nearby stations that it is going to change the TBTT,using the ALERT field of the beacon to be transmitted, performs a scan,finds a new available TBTT where collision will not occur, and changesthe TBTT of the local station to the available TBTT.

On the other hand, the STA0 continues beacon transmission as if nothinghad happened, but there are cases wherein the STA0 performs scanningprocessing to know the state of the network, having recognized that thenetworks have crossed from reception of the beacon of the STA2.

FIG. 34 illustrates an example of a case wherein collision has occurredbetween the transmitted signal of the STA0 and the beacon transmissionpoint-in-time of the STA2.

The STA0 transmits an RTS to the STA1 at point-in-time T0, and data atthe point-in-time T1. The STA2 is attempting to transmit the beacon atpoint-in-time T2, and accordingly is operating the receiving deviceaccording to Listen Before Send, and thus can receive signals of theSTA0. Also, the STA2 follows CSMA/CA procedures and refrains from signaltransmission while signals of other stations are present. Further, theSTA2 analyzes the Duration field of the received signals, andaccordingly refrains from transmission of signals upon point-in-time T3where an ACK is received. Consequently, the scheduled transmission of abeacon at point-in-time T2 is delayed.

At this point, the STA2 has already detected that signals periodicallytransmitted are colliding. Following elapsing of PIFS (or SIFS)+a randomdelay amount (e.g., TBTT offset) from point-in-time T3, the STA2 makestransition to a signal transmittable state, and transmits a beacon atpoint-in-time T4. At this time, the STA2 lists in the TOIS field that itcould not transmit a beacon at the point-in-time intended by the localstation.

The STA0 operates the receiving device before and after signaltransmission, and recognizes by Listen After Send that the STA2 hastransmitted a beacon immediately following signals of the local station,thereby confirming the presence of the STA2. Also, the fact that thetransmitting station was not able to transmit at the intendedpoint-in-time can be recognized by referencing the TOIS field in thebeacon received form the STA2, and determines that the signaltransmitted from itself has interrupted the beacon transmissionpoint-in-time, thereby detecting signal collision.

In the event that the STA2 recognizes for some reason that the signalsof the STA0 are being received in a TPP (such as being transmittedfollowing an auxiliary beacon, or description being made in a part ofthe transmitted signals to the effect of a TPP), there are cases whereinthe STA2 may change the TBTT of itself. On the other hand, in the eventthat the STA2 does not change the TBTT due to the signals of the STA0not being received in a TPP or the like, the STA0 recognizes thatbeacons of the STA2 are being transmitted near this TBTT, andaccordingly the STA0 forbids transmission in order to not obstructbeacon transmission of the STA2 from now on.

The STA0 and the STA2 can recognize that networks have crossed, bydetecting mutual collision. In such cases, the stations may perform scanprocessing to know the state of the network.

FIG. 35 illustrates an example of a case wherein collision has occurredbetween signal reception of the STA0 and the beacon transmissionpoint-in-time of the STA2.

The STA0, which is the data originator, transmits a CTS to the STAT atpoint-in-time T1. with point-in-time T1 as a TBTT, the STA2 isattempting to transmit the beacon at point-in-time T2 which is laterthan this point-in-time by a TBTT offset, and is operating the receivingdevice according to Listen Before Send, and thus can receive CTSsignals. The STA2 follows CSMA/CA procedures and refrains from signaltransmission while signals of other stations are present. Further, theSTA2 analyzes the Duration field of the received signals, andaccordingly refrains from transmitting signals upon point-in-time T3where data is received. Consequently, the beacon which was originallyscheduled to be transmitted at point-in-time T2 is delayed.

At this point, the STA2 has already detected that signals periodicallytransmitted are colliding. Following elapsing of PIFS (or SIFS)+a randomdelay amount (e.g., TBTT offset) from point-in-time T3, the STA2 makestransition to a signal transmittable state, and transmits a beacon atpoint-in-time T4. At this time, the STA2 lists in the TOIS field that itcould not transmit a beacon at the point-in-time intended by the localstation.

The STA0 operates the receiving device before and after signaltransmission, and recognizes by Listen After Send that the STA2 hastransmitted a beacon immediately following reception of the signals ofthe local station, thereby confirming the presence of the STA2. Also,the fact that the STA2 was not able to transmit at the intendedpoint-in-time can be recognized by referencing the TOIS field in thebeacon received form the STA2, and determines that the signaltransmitted from itself has interrupted the beacon transmissionpoint-in-time of the STA2, thereby detecting signal collision.

In the event that the STA2 recognizes for some reason that the signalsof the STA0 are being received in a TPP (such as being transmittedfollowing an auxiliary beacon), there are cases wherein the STA2 maychange the TBTT, i.e., beacon transmission position of itself. On theother hand, in the event that the STA2 does not change the TBTT due tothe signals of the STA0 not being received in a TPP or the like, theSTA0 recognizes that beacons of the STA2 are being transmitted near thisTBTT, and accordingly activates procedures for forbidding transmissionto the STA1 in order to not obstruct beacon transmission of the STA2from now on, so that the STA0 does not perform reception in this timespan.

The STA0 and the STA2 can recognize that networks have crossed, bydetecting mutual collision, and may perform scan processing to know thestate of the network.

With the example described with reference to FIG. 34, description hasbeen made assuming that the communication stations recognize theDuration field. Though recognition of the Duration field is preferableprocessing, a description will be made of collision detection regardinga case wherein recognition of the Duration field is not performed. FIG.36 illustrates an example of a case wherein the signal transmission ofthe STA0 and the beacon transmission point-in-time of the STA2 havecollided.

The STA0 transmits data, and the TBTT of the STA2 (point-in-time T1 inthe drawing) arrives while performing this data transmission. The STA2attempts beacon transmission at point-in-time T1, and receives signalsfrom the STA0 since the receiving device is operating in accordance withListen Before Send. The STA2 follows the CSMA procedures to refrain fromsignal transmission while signals of other stations are present, andtransmission is forbidden to point-in-time T2. Consequently, the beacontransmission that was originally schedule for point-in-time T1 isdelayed.

At this point, the STA2 has already detected that signals periodicallytransmitted are colliding. Following elapsing of DIFS+a random delayamount (e.g., TBTT offset) from point-in-time T2, the STA2 makestransition to a signal transmittable state, and transmits a beacon atpoint-in-time T3. At this time, the STA2 lists in the TOIS field that itcould not transmit a beacon at the point-in-time intended by the localstation.

The STA0 receives an ACK from the STA1 during this time, and in theevent that the DIFS is longer than the time necessary for receiving theACK, a situation wherein the STA2 obstructs reception of the ACK willnot occur. The STA0 operates the receiving device before and aftersignal transmission, and accordingly receives the beacon which the STA2transmits at point-in-time T3 by Listen After Send, and thus can confirmthe presence of the STA2. Also, the STA0 can recognize by referencingthe TOIS field of the beacon received from the STA2 that the STA2 is notable to transmit at the point-in-time intended, judges that the signaltransmitted from itself has obstructed the beacon transmissionpoint-in-time of the STA2, and thus detects signal collision.

In the event that the STA2 recognizes for some reason that the signalsof the STA0 are being received in a TPP (such as being transmittedfollowing an auxiliary beacon, a description being made in a part of thesignals transmitted from the STA0 to the effect that transmission isbeing made in a TPP, etc.), there are cases wherein the STA2 may changethe TBTT, i.e., beacon transmission position of itself. On the otherhand, in the event that the STA2 does not change the TBTT due to thesignals of the STA0 not being received in a TPP or the like, the STA0recognizes that beacons of the STA2 are being transmitted near thisTBTT, and accordingly transmission is forbidden for the STA0 to transmitin this time span, in order to not obstruct beacon transmission of theSTA2 from now on.

The STA0 and the STA2 can recognize that networks have crossed, bydetecting mutual collision, and may perform scan processing to know thestate of the network.

Note that with the above-described processing, the rule is that at thetime of beacons colliding, a communication station which has received abeacon from another station immediately prior to its own beacontransmission point-in-time is to change its own beacon transmissionpoint-in-time, however, a reverse arrangement may be made wherein acommunication station which has received a beacon from another stationimmediately following its own beacon transmission point-in-time is tochange its own beacon transmission point-in-time.

Example of Operation of Collision Avoiding Procedures

Next, another example will be given to describe collision detection in acase wherein Duration field recognition is not performed or RTS/CTSprocedures as not used together, as with the operation example shown inFIG. 36. FIG. 37 illustrates an example of a case wherein the signalreception of the STA0 and the beacon transmission point-in-time of theSTA2 have collided.

The STA0 receives data from the STA1 which is the data originator. TheTBTT of the STA2 (point-in-time T1 in the drawing) arrives in the midstof this data transmission. The STA2 is operating the receiving devicebefore signal transmission (beacon transmission) due to Listen BeforeSend, but cannot directly receive transmitted data from the STA1 whichis a hidden terminal, and accordingly has not yet detected the presenceof the STA0, and accordingly transmits a beacon at point-in-time T1 onschedule.

The STA0 receives interference in the signals reception from the STA1due to the beacon signal transmission from the STA2, and cannot receivethe data correctly. Following data reception, the STA0 returns a messageto the STA1 to the effect that the data could not be received, in theform of a NACK.

The STA2 operates the receiving device for a certain while followingsignal transmission according to Listen After Send, and accordingly canreceive the NACK of the STA0. The STA2 judges that the STA1 has failedin data reception due to its own signal transmission, from receiving theNACK from the STA1 immediately following signal transmission fromitself, and thereby detects that the beacon from itself has collidedwith signal reception at another station.

Immediately following this, the STA2 may transmit signals (not shown) tothe STA0 to notify the STA0 “that this time span is being used forbeacon transmission of the STA2”, so as to prompt changing of the signalreception timing of the STA0. On the other hand, in the event that theSTA2 does not perform this, there a cases wherein the STA2 autonomouslychanges the TBTT.

The STA2 (and the STA0) can recognize that networks have crossed, bydetecting mutual collision, and may perform scan processing to know thestate of the network.

While description has been made with reference to FIG. 33 through FIG.37 regarding cases of collision between signals of other stations andbeacons, exactly the same procedures are performed in cases of collisionbetween signals of other stations and signals of preferentialtransmission/reception performed periodically.

In a case wherein beacon collision has occurred due to change in therange of reach of airwaves, the following supplementary items arefurther taken into consideration in the event of performing collisionavoidance using the above procedures wherein one of the communicationstations which has caused collision moves the beacon transmissionpoint-in-time (TBTT change) as described above.

In the above-described example, upon receiving a beacon of anotherstation immediately prior to transmission of its own beacon, the STA0activates TBTT changing processing immediately, but an arrangement ismade wherein TBTT changing processing is not activated as an exceptionin the event that the STA0 has just recently set a new TBTT. The phrase“just recently” as used here is equivalent to 1 through 3 super framesfollowing setting the new TBTT, for example. The reason is that, in theevent that relatively large networks collide, there is the possibilitythat collision will be avoided by TBTT change performed by othercommunication stations, and standing by until the abnormal situation isstabilized is appropriate. Also, there is also the possibility that thenetwork with which collision is occurring will go away, the abnormalsituation thereby being stabilized.

Further, TBTT changing processing is not activated as an exception inthe event that a beacon of another station is received immediately priorto beacon transmission of the local station but the ALERT field in thereceived beacon notifies information to the effect that the TBTT of thebeacon is going to be changed. This is because the beacon collision willbe solved by itself due to the TBTT changing processing.

Taking into consideration these supplementary items contributes topreventing oscillation in TBTT changing in the event of multiplecommunication stations simultaneously changing their TBTTs.

Also, TBTT changing processing is not activated as an exception in theevent that a beacon of another station is received immediately prior tobeacon transmission of the local station but the priority valueindicated in the TYPE field of the received beacon is lower than thepriority value of the beacon of the local station transmitted at theTBTT. In this case, this means that the station transmitting the beaconwith lower priority value activates TBTT changing processing instead.For example, in the event a normal beacon of one communication stationcollides with an auxiliary beacon of another communication station, theTBTT for the auxiliary beacon needs to be moved. Also, in the event thatauxiliary beacons collide one with another, the one with higher trafficpriority is given preference, and the one with lower priority should bemoved (or eliminated).

FIG. 13 illustrates, in the form of a flowchart, device actions executedat each communication station, in a case wherein beacon collision hasoccurred due to change in the range of reach of airwaves, to avoidbeacon collision by one of the communication stations which has causedthe collision moving the beacon transmission point-in-time (TBTTchange). Such device actions are actually realized in the form ofexecuting a predetermined execution command program at the centralcontrol unit 103 within the wireless communication device 100.

The actions are activated in response to the communication stationdetecting collision of beacons transmitted from the local station.First, the local station checks whether or not a TBTT change hasoccurred recently within itself (step S1).

In the event that no TBTT change has been made recently, a check isfurther made regarding whether or not a description is made in the ALERTfield of the received beacon to the effect that the TBTT is going to bechanged (step S2).

In the event that no recent TBTT change has been confirmed at the localstation or at nearby stations in steps S1 and S2, the priority of thetransmitted beacon of the local station side and the priority describedin the Type field of the received beacon are compared (step S3).

In the event that the priority of the beacon received from the otherstation is not lower than the priority of the transmitted beacon of thelocal station side, a check then is conversely made regarding whether ornot the priority of the beacon received from the other station is higherthan the priority of the transmitted beacon of the local station side(step S4).

In the event that the priority of the beacon received from the otherstation is higher than the priority of the transmitted beacon of thelocal station side, determination is made to change the TBTT, i.e., thebeacon transmission position, of the local station. In this case, thecommunication station executes scanning for at least one super frame tocollect information for determining the new TBTT, and makes notificationto the nearby stations with a beacon describing in the ALERT field amessage to the effect that the TBTT will be changed, as described withreference to FIG. 11, and further, discovers an available TBTT with theprocedures described above with reference to FIG. 9, so as to detect adestination to move the beacon (step S6). Transmission is made with abeacon from the new TBTT, thereby notifying the nearby stations of therelocated beacon transmission timing.

Also, in step S4, in the event that the priority of the beacon receivedfrom the other station is not higher than the priority of thetransmitted beacon of the local station side, i.e., in the event thatthe priority of both beacons matches, a check is made regarding whetheror not the reception point-in-time of the received beacon is earlierthan the beacon transmission point-in-time of the local station (stepS5).

In the event that the timing of the beacon received from the otherstation is earlier, the local station determines to change its own TBTT,i.e., beacon transmission position, the reason being that a beacon ofanother station has been received immediately prior to transmission ofits own beacon. That is to say, the communication station executesscanning for at least one super frame to collect information fordetermining the new TBTT, makes notification to the nearby stations witha beacon describing in the ALERT field a message to the effect that theTBTT will be changed, and further discovers an available TBTT so as todetect a destination to move the beacon (step S6). Transmission is thenmade with a beacon from the new TBTT, thereby notifying the nearbystations of the relocated beacon transmission timing.

Collision Avoiding Procedures in Case that Signal Transmission TimingsCompletely Match:

So far, description has been made under the assumption that beacontransmission and transmission/reception prioritized periods TPPs startwith a slight random delay from a point-in-time based on a TBTT. Aclassical case enables the signals of both to be discovered at the timeof collision even in the event that the transmission timing TBTTs of thesignals within the super frame are the same, due to this random delay.However, a situation can occur wherein, in some cases, in addition tothe TBTTs of the colliding signals, even the random values completelymatch. In such a case, the colliding signals are always transmitted atthe same timing, and the communication stations which have caused thecollision cannot detect the signals of each other since both areperforming transmission operations, and accordingly cannot recognizethat the signals are colliding at this time span.

In such a case, the quality of the signals transmitted/received in theparticular time span where collision is occurring markedly deteriorates,so communication cut-off occurs in this time span alone. Accordingly,there are cases wherein, upon a communication station judging that thequality of signals transmitted from the TPP in a particular time spanhave markedly deteriorated, collision of signals can be resolved byreleasing the TPP at this time span.

Examples of phenomenon used for judging marked deterioration is signalquality include a great number of errors occurring in only a particulartime span leading to a continued communication cut-off state, no ACKsbeing returned during only the particular time span, communication beingrequested at a low data rate during only the particular time span, andso forth.

A communication station which has released the TPP due to such a reasoncontinues transmission/reception of data with access method based onCSMA/CA with a random backoff, and also activates scanning processing bycontinuously operating the receiving device, to attempt detection ofbeacon signals and the like of another station which may be hidden. Upondiscovering the beacon of a new communication station is this process,the above-described procedures are followed to analyze the informationdescribed in the beacon, extract the media occupation state of theneighboring communication stations, and effect collision avoidance.

FIG. 38 illustrates, in flowchart form, the communication proceduresincluding collusion avoiding operations in the case in which even therandom values in addition to the TBTTs of colliding signals completelymatch.

The communication station sets the signal transmission timing TBTT ofthe beacon or Transmission Prioritized Period TPP in the super frame(step S31), and performs signal transmission/reception based on the settransmission timing (step S32).

The communication station performs transmission operations at thetransmission timing TBTT, and accordingly cannot detect collision byitself in the event that not only TBTTs but also the random values,i.e., the TBTT offsets completely match. Accordingly, periodictransmission operations of the signals continues over several superframes. Consequently, the situation in which the signal quality hasmarkedly deteriorates is detected (step S33). Deterioration of qualityas used here is detected by symptoms such as a great number of errorsoccurring in only a particular time span leading to a continuedcommunication cut-off state, no ACKs being returned during only theparticular time span, communication being requested at a low data rateduring only the particular time span, and so forth.

Upon detecting such signal quality deterioration, the communicationstation searches the transmission/reception timings for others which canbe used within the super frame (step S34), if found releases thetransmission section with deteriorated quality (step S35), and sets thedeteriorated periodic transmission signals to the new transmissiontiming TBTT.

the new transmission timing TBTT can be notified to nearby station bydescribing in a beacon, and also by transmitting periodic signals withthe new transmission timing TBTT itself.

Collision Avoiding Procedures in Case that Normal Beacon Cannot beReceived:

There are cases wherein not all the information described in the normalbeacon is included in auxiliary beacons or signals periodicallytransmitted and received using Transmission Prioritized Periods TPPs(see FIG. 7). In this case, even in the event that the is collisionbetween auxiliary beacons one with another, collision between signalsperiodically transmitted and received using Transmission PrioritizedPeriods TPPs and beacons, or collision between signals periodicallytransmitted/received one with another, media occupation information forother time spans cannot be detected. Also, cases can be conceivedwherein normal beacons cannot be received even by performing scanningprocessing, due to transmitting other signals at the normal beacontransmission time span of the communication station owing to even theTBTT offsets coincidentally completely matching.

In such a case, an arrangement may be made wherein a Serial field isprovided in the auxiliary beacons or signals periodically transmittedusing Transmission Prioritized Periods TPPs to describe relativepoint-in-time information indicating what number in order TBTT thesignal is being transmitted at based on the normal beacon of the localstation, whereby a communication station which has received auxiliarybeacons or signals periodically transmitted can extract the normalbeacon transmission point-in-time of the auxiliary beacon transmittingstation.

FIG. 39 illustrates a communication operation example for performingsignal collision avoiding, based on the contents of the Serial fieldadded to the auxiliary beacons or periodically-transmitted signals. Inthe drawing, the assumption is that the STA0 and the STA1 are incommunication with other unshown communication stations, and have beenoperating as mutually independent networks, but the STA0 and the STA1have come into the range of reach of airwaves due to the communicationstations moving or an obstacle shielding the networks one from anotherbeing removed. Also, in the drawing, 8 TBTTs are set in the super frame,T0 through T7.

The top tier in FIG. 39 is the initial state. At point-in-time T0 andpoint-in-time T2, the normal beacons of both sides are colliding withthe auxiliary beacons of the other. Now, let us assume a case whereinreception of the normal beacons of each other is continuously impossibledue to a reason such as the TBTT offset continuing to match. In thiscase, the STA1 cannot receive the normal beacons of the STA0, andneither can the STA0 receive the normal beacons of the STA1.

Subsequently, the STA1 can receive auxiliary beacons and signalsperiodically transmitted using Transmission Prioritized Periods TPPsfrom the STA0, transmitted at point-in-time T4 and point-in-time T6. Inthis case, upon the STA1 receiving an auxiliary beacon transmitted fromthe STA0 at point-in-time T4 and point-in-time T6, the STA1 analyzes thedescription in the Serial field, and extracts information regarding howmuch of a relative time difference the auxiliary beacon is beingtransmitted at from the normal beacon transmission point-in-time,thereby recognizing that the normal beacon of the STA0 is beingtransmitted near the point-in-time T2. Further, the STA1 recognizes thatit is transmitting signals near the point-in-time T2 itself, andaccordingly cannot receive the normal beacons of the STA0.

Subsequently, as shown in the upper-middle tier in the drawing, the STA1releases the TPP used near the point-in-time T2 and repositions toanother TBTT (point-in-time T3 in the drawing), so as to be capable ofreceiving the normal beacons of the STA0. The STA1 can tell the resourceusage state of the STA2 by receiving the normal beacons of the STA2.

The STA0 can also receive the auxiliary beacons of the STA1 transmittedat point-in-time T5, and by performing processing the same as that ofthe STA1 described above, can receive the normal beacons of the STA1 byreleasing its own TPP at point-in-time T0. Finally, the placement ofnormal beacons and auxiliary beacons (periodic signal transmission usingTransmission Prioritized Periods or TPPs) such as shown at the bottomtier in FIG. 39 is achieved.

On the other hand, in the event that the STA0 does not autonomouslyrelease the TPP, such as the STA0 not noticing the auxiliary beacon ofthe STA1 at point-in-time T5, a message may be transmitted from the STA1to the STA0 to the effect that it should release the TPP, as show at thelower-middle tier in FIG. 39, for example. In this case, upon receivingthis release request message, the STA0 changes the transmissionpoint-in-time of the auxiliary beacon which had been transmitted atpoint-in-time T0, and finally, the placement of normal beacons andauxiliary beacons such as shown at the bottom tier in FIG. 39 isachieved. Accordingly, the STA0 can receive the normal beacons of theSTA1, and thereby can tell the resource usage state of the STA1.

Note that the TPP section changing procedures by auxiliary beacon areperformed according to already-descried procedures. Following detectionof an available slot by scanning operations, TPP placement is performedat a point-in-time where collision does not occur.

Other Scan Triggers

Description of scanning operations has been made so far regardingscanning performed periodically, and scanning performed due to detectionof collision. With the present embodiment, there are cases whereinsignals of a communication station which had not been recognized as aneighboring station so far can be detected by signal detection/receptionprocessing performed before signal transmission (Listen Before Send) andsignal detection/reception processing performed after signaltransmission (Listen After Send), even in the event that collision isnot detected. There are cases wherein scanning processing is activateddue to such signal detection/reception processing, beacons of thecommunication station are searched for, and acquisition of mediaoccupation information of the communication station is attempted.

Also, the signal detector and receiving device are continuous operatedduring scanning processing in time spans when signals are not beingtransmitted, but signal transmission is given preference during the timespan for transmitting signals, and the receiving device may be stoppedfor just the duration of signal transmission.

F. Other Beacon Collision Scenarios and Collision Avoiding Procedures

In the above section E, description has been made regarding processingprocedures for avoiding beacon collision in a case wherein the range ofreach of airwaves changes due to communication stations moving and soforth. Besides, this, a case can be conceived wherein the electric powerof a new communication station turns on, thereby exposing collision ofbeacons transmitted by the communication stations.

FIGS. 14A-14D illustrate the way in which beacons transmitted by thecommunication stations collide due to the power of a new communicationstation being turned on. The drawings illustrate an example whereinsystems configuring networks already existing independently are mergeddue to the emergence of a new communication station. Also, even if a newcommunication station does not emerge, there are cases wherein systemsconfiguring already-existing networks are merged due to a thirdcommunication station coming therebetween. In such a case as well, thesame processing as described below can be performed.

At FIG. 14A, communication stations the STA0 and the STA1 exist in arange where airwaves from communication stations the STA2 and the STA3cannot reach, with the STA0 and the STA1 performing communication. Also,the STA2 and the STA3 perform communication completely independent fromthese. In this case, the beacon transmission timings are set for eachcommunication station in a independent manner for each system, but asshown in FIG. 14B, beacon transmission timings which unfortunately matchhave been set between the stations which do not recognize each other.

Subsequently, upon the communication station the STA4 newly emergingbetween these communication station, and assuming that the stations theSTA0, the STA1, the STA2, and the STA3 have become capable oftransmission/reception with the STA4, as shown in FIGS. 14C-14D, thebeacons of the stations collide as far as the STA4 is concerned. In sucha case, there is the need for at lease one of the sets of stations ofwhich the beacons are colliding to change the beacon transmission timingTBTT, otherwise, the beacons cannot be heard correctly. In other words,the STA4 cannot participate in the network.

In such a case as well, there is the need for a station to change thetransmission point-in-time. FIG. 15 shows an example of TBTT changingprocedures in the event that beacon collision has been exposed due toparticipation of a new communication station. The example shown here isa case wherein the TBTT of the beacon transmitted by the STA0 and theTBTT of the beacon transmitted by the STA2 have approximately matchedthe TBTT0, but the TBTT of the STA0 is slightly later. Also, we will saythat the STA4 is capable of communication with either of the STA0 andthe STA2, but the STA0 and the STA2 are in a state wherein directcommunication cannot be made (hidden terminals from each other).

At point-in-time T0, the beacon transmission TBTT for both the STA0 andthe STA2 arrives, so each transmit beacons at a point-in-time shiftedfrom the point-in-time T0 by a TBTT offset. At point-in-time T0, theTBTT offset of the STA0 and the TBTT offset of the STA2 happen to bedifferent values, with a small TBTT off set value being selected for theSTA2, and a large TBTT off set value being selected for the STA0.

The STA4 can receive beacons transmitted from both the STA0 and theSTA2. Now, the STA4 has received beacons from these two station withinthe TBTT incrementation of itself (i.e., within the range of±B_(min)/2), and accordingly can detect that beacons are colliding.Next, determination is made on which communication station a messageshould be transmitted regarding requesting changing of the TBTT. Withthe example shown in the drawing, the beacon of the STA0 was receivedlater, so the STA4 determines to have the STA0 to change the TBTT, andtransmits the STA0 a message M requesting changing of the TBTT. Now,even in the event that the STA0 and the STA2 are not transmitting orreceiving data and are in a power saving state, as described earlierboth are required at the time of signal transmission to performreception operations for a predetermined period before and followingtransmission of signals from the local station, (Listen BeforeSend/Listen After Send), so the STA0 can receive this message.

Note that the STA4 does not simply compare the beacon receptionpoint-in-time as such to determine which of the received beacons thathave collided is later, but rather makes reference to the TOIS fields ofthe beacons, and subtracts the pseudo-random sequence used, therebycalculating the TBTT of the beacon itself. Of course, an agreement maybe made wherein the TBTT changing message is transmitted to the sidewith the earlier beacon reception point-in-time or TBTT, so long as thesame agreement is held among all of the communication stations, butdescription will proceed here with the example of an agreement whereinthe message is sent to the later one.

Upon receiving the TBTT change request message and recognizing that itmust change its TBTT, the STA0 activates the TBTT changing processingfrom point-in-time T1. In this case, with these processing procedures,the STA0 first makes notification to the nearby stations that it isgoing to change the TBTT, using the ALERT field of the beacon to betransmitted (the ALERT field is a field for storing information to betransmitted to the nearby stations in an abnormal situation). Further,the STA0 executes scanning for at least one super frame, to collectinformation for determining the new TBTT. With the example shown in FIG.15, the TBTT changing processing is immediately activated frompoint-in-time T1, but this processing may be executed after a delay ofone or two super frames, due to delay in processing within thecommunication station.

Upon the STA0 finding an available TBTT by the procedures described withreference to FIG. 9, the TBTT1 is set as the new TBTT, and does notperform beacon transmission at point-in-time T2 but instead performsbeacon transmission at point-in-time T3 instead, and subsequentlyperiodically performs beacon transmission at the timing of TBTT1 with aTBTT offset.

On the other hand, the STA2 transmits its beacon at point-in-time T2 asif nothing had happened, and subsequently continues to transmit itsbeacon at the timing of TBTT0 with a TBTT offset.

In the event that a communication station recognizes a beacon notifyingin the ALERT field that the TBTT is to be changed, or recognizes that nobeacon is being transmitted near the TBTT of beacons received so far, ascan is executed to tell where the new TBTT of the beacon has beendetermined at (not shown).

In a case wherein beacon collision has become exposed due toparticipation of a new communication station or the like, the followingsupplementary items are further taken into consideration in the event ofperforming collision avoidance using the above procedures wherein thenewly-participating station requests one of the communication stationswhich has caused collision to change the beacon transmissionpoint-in-time as described above.

In the above-described example, upon receiving a TBTT change requestfrom the STA4, the STA0 activates TBTT changing processing immediately,but an arrangement is made wherein TBTT changing processing is notactivated as an exception in the event that the STA0 has just recentlyset a new TBTT. The phrase “just recently” as used here is equivalent to1 through 3 super frames following setting the new TBTT. The reason isthat, in the event that relatively large networks collide, there is thepossibility that collision will be avoided by TBTT change performed byother communication stations, and standing by until the abnormalsituation is stabilized is appropriate. Also, there is also thepossibility that the network with which collision is occurring will goaway, the abnormal situation thereby being stabilized.

Further, with the above example, the STA4 transmits a TBTT changerequest message to the communication station with the later collisionbeacon reception point-in-time or the later TBTT, but in the event thatthe ALERT field in one of the colliding beacons notifies information tothe effect that the TBTT of the beacon is going to be changed, thisbeacon is not counted as a colliding beacon, so the TBTT change requestmessage transmission processing is activated only in the event thatthere are colliding beacons excluding these. This is because the beaconcollision will be solved by itself due to the TBTT changing processing.

Taking into consideration these supplementary items contributes topreventing oscillation in TBTT changing in the event of multiplecommunication stations simultaneously changing their TBTTs.

Also, in the event that the priority values indicated in the TYPE fieldsof the colliding beacons differ, the TBTT change request messagetransmission processing is activated excluding beacons indicating apriority value greater than the lowest priority value thereof fromstations to which the message is to be transmitted to. For example, inthe event a normal beacon of one communication station collides with anauxiliary beacon of another communication station, the TBTT for theauxiliary beacon should be moved. Also, in the event that auxiliarybeacons collide one with another, the one with higher traffic priorityis given preference, and the one with lower priority should be moved (oreliminated).

FIG. 16 illustrates, in the form of a flowchart, device actions executedat each communication station, in a case of beacon collision beingexposed due to participation of a new communication station or the like,wherein the newly-participating station requests one of thecommunication stations which has caused collision to change the beacontransmission point-in-time (TBTT change), to avoid beacon collision.Such device actions are actually realized in the form of executing apredetermined execution command program at the central control unit 103within the wireless communication device 100.

The actions are activated in response to the communication stationdetecting collision of beacons transmitted from the local station. Wewill say here that reception of beacon A and beacon B have collided.

First, a check is made regarding whether or not one of the receivedbeacons A or B has described in the ALERT field that the TBTT will bechanged, and beacons with this description are deleted from collidingbeacons (step S10).

Now, following deleting beacons having described in the ALERT field thatthe TBTT will be changed from colliding beacons, determination is madeonce more regarding whether or not there are colliding beacons (stepS11). In the event that colliding beacons are found to exist as a resultof the determination, the later-described processing of step S12 and onis performed, and in the event that no colliding beacons are found toexist, this processing routine ends.

In the event that colliding beacons still exist even following theprocessing in step S10, the TYPE fields of each of the received beaconsare referred to, and the difference in traffic priority is compared(step S12).

Now, in the event that the priority of beacon A is lower, a TBTT changerequest message is transmitted to the originator of the beacon A (stepS14), and this processing routine ends. Also, in the event that thepriority of beacon B is lower, a TBTT change request message istransmitted to the originator of the beacon B (step S15), and thisprocessing routine ends.

Also, in the event that there is no difference in the priority of thereceived beacons, determination is further made with regard to whichreceived beacons has arrived later (step S13). The beacon receptionpoint-in-time as such is not compared to determine which of the receivedbeacons that have collided is later, but rather reference is made to theTOIS fields of the beacons, and subtracts the pseudo-random sequenceused, thereby calculating the TBTT of the beacons themselves.

Now, in the event that beacon A has arrived later, a TBTT change requestmessage is transmitted to the originator of the beacon A (step S14), andthis processing routine ends. Also, in the event that beacon B hasarrived later, a TBTT change request message is transmitted to theoriginator of the beacon B (step S15), and this processing routine ends.

Collision Avoiding Procedures in Case that Normal Beacon Cannot beReceived:

There are cases wherein not all the information described in the normalbeacon (see FIG. 7) is included in auxiliary beacons or signalsperiodically transmitted and received using Transmission PrioritizedPeriods TPPs (same as above). In this case, even in the event that theis collision between auxiliary beacons one with another, collisionbetween signals periodically transmitted and received using TransmissionPrioritized Periods TPPs and beacons, or collision between signalsperiodically transmitted/received one with another, media occupationinformation for other time spans cannot be detected. Also, cases can beconceived wherein normal beacons cannot be received even by performingscanning processing, due to coincidental transmission of other signalsat the normal beacon transmission time span of the communicationstation.

In such a case, an arrangement may be made wherein a Serial field isprovided in the auxiliary beacons or signals periodically transmittedusing Transmission Prioritized Periods TPPs to describe relativepoint-in-time information indicating what number in order TBTT theauxiliary beacon is being transmitted at based on the normal beacon ofthe local station, whereby a communication station which has receivedauxiliary beacons or signals periodically transmitted can extract thenormal beacon transmission point-in-time of the auxiliary beacontransmitting station.

FIG. 40 illustrates a communication operation example for performingsignal collision avoiding, based on the contents of the Serial fieldadded to the auxiliary beacons or periodically-transmitted signals. Inthe drawing, the assumption is that the STA0 is in communication withanother unshown communication station, the STA2 is also in communicationwith another unshown communication station, and both have been operatingas mutually independent networks, but the STA1 has come into the rangeof reach of airwaves of the STA0 and the STA2 due to communicationstations moving or an obstacle shielding the networks one from anotherbeing removed. Also, in the drawing, 8 TBTTs are set in the super frame,T0 through T7.

The top tier in FIG. 40 is the initial state. At point-in-time T0, theauxiliary beacons of the STA0 and the normal beacon of the STA2 arecolliding. Now, the STA1 cannot receive the normal beacons of the STA2at point-in-time T0, due to the auxiliary beacons or signalsperiodically transmitted using Transmission Prioritized Periods TPPstransmitted from the STA0. However, the auxiliary beacons of the STA2transmitted at point-in-time T5 can be received. In this case, upon thereceiving an auxiliary beacon transmitted from the STA2 at point-in-timeT5, the STA1 analyzes the description in the Serial field thereof, andextracts information regarding how much of a relative time differencethe auxiliary beacon is being transmitted at from the normal beacontransmission point-in-time, thereby recognizing that the normal beaconof the STA2 is being transmitted near the point-in-time T0. Further, theSTA1 recognizes that the STA0 is transmitting signals near thepoint-in-time T0, and accordingly cannot receive the normal beacons ofthe STA2.

Subsequently, as shown in the middle tier in FIG. 40, the STA1 transmitsa message to the STA0 to release the Transmission Prioritized Period TPPacquired by the STA0 near the point-in-time T0. Upon receiving thismessage, the STA0 releases the TPP held at the point-in-time T0.Accordingly, only the normal beacon of the STA2 is transmitted as aperiodic transmitted signal at point-in-time T0, and the STA1 canreceive the normal beacons of the STA2. The STA1 can tell the resourceusage state of the STA2 by receiving the normal beacons of the STA2.

On the other hand, as shown in the bottom tier in FIG. 40, there arecases wherein the STA1 transmits a message requesting normal beacontransmission point-in-time change to the STA2. In this case, uponreceiving this message, the STA2 activates transmission changingprocedures for the normal beacon which had been transmitted atpoint-in-time T0, and following detection of an available slot by thealready-described procedures, normal beacon transmission is started at apoint-in-time where collision does not occur. Accordingly, the STA1 canreceive the normal beacons of the STA2, and the STA1 can tell theresource usage state of the STA2.

Other Scan Triggers:

Description of scanning operations has been made so far regardingscanning performed periodically, and scanning performed due to detectionof collision. With the present embodiment, there are cases whereinsignals of a communication station which had not been recognized as aneighboring station so far can be detected by signal detection/receptionprocessing performed before signal transmission (Listen Before Send) andsignal detection/reception processing performed after signaltransmission (Listen After Send), even in the event that collision isnot detected. There are cases wherein scanning processing is activateddue to such signal detection/reception processing, beacons of thecommunication station are searched for, and acquisition of mediaoccupation information of the communication station is attempted.

Also, the signal detector and receiving device are continuous operatedduring scanning processing in time spans when signals are not beingtransmitted, but signal transmission is given preference during the timespan for transmitting signals, and the receiving device may be stoppedfor just the duration of signal transmission.

G. Setting TBTT of Auxiliary Beacon Based on Priority

At the time of transmitting beacons, a communication station performsscanning, finds available TBTTs by referring to the NBOIs of receivedbeacons, and sets its own new TBTT.

However, situations can be conceived wherein the super frame is alreadysaturated with normal beacons and auxiliary bacons of other stations inthe processing of setting the new TBTT, so that there is no availableTBTT. In this case, the communication station can solve the situation byabandoning sending traffic out on this system, or by competing forresources used for transmitting traffic with lower order of preference,so as to transmit traffic if the local station with high order ofpreference. The wireless network according to the present embodimenttakes the latter method, and accordingly is permitted to request anothercommunication station to stop transmitting auxiliary beacons with loworder of preference.

FIG. 17 illustrates, in the form of a flowchart, the procedures for acommunication station to set a new TBTT within a super frame cycle. Suchdevice actions are actually realized in the form of executing apredetermined execution command program at the central control unit 103within the wireless communication device 100.

These procedures are activated for setting a TBTT for a normal beaconwithin the super frame at the time of new participation, or for settinga TBTT for an auxiliary beacon within the super frame in order toacquire traffic resources (step S21). We will say that the priority ofthe beacon for which the local station is attempting to set a TBTT hasbeen set at this point.

The communication station performs a scanning operation for at least onesuper frame (step S22), and searches for an available new TBTT slotwithin the super frame (step S23). In the event that an available slothas been found here, the new TBTT is set following the proceduresdescribed with reference to FIG. 9 (step S27), and this entireprocessing routine is ended.

On the other hand, in the event that an available slot cannot bedetected within the super frame, i.e., in a full state, thecommunication station searches the beacons which have TBTTs paced withinthe super frame for one which has an order of preference lower than thatof the beacon for which the local station is attempting to set a TBTT(step S24).

In the event that a desired number of beacons with low order ofpreference has been detected, a stop request for the beacon transmissionis performed to the originators of the beacons (step S25).

Subsequently, the communication station sets the TBTT for its own normalbeacon or auxiliary beacon at the position which has become an availableslot due to the beacon transmission stopping (step S26), and the entireprocessing routine ends.

FIG. 18 illustrates the procedures for searching for the beacon with thelowest order of preference from the beacons with TBTTs placed in thesuper frame, and setting a TBTT for the beacon of the local station.Now, the TBTTs of the beacons which the nearby stations set arerecognized by referencing the NBOI field described in each beacon. Also,the priority of the beacon is described in the TYPE field of the beacon.

The example shown in FIG. 18, is described from the perspective of acommunication station A which desires to newly transmit traffic withhigher order of preference, with a communication environment whereinnearby the communication station A are a communication station 0,communication station 1, and communication station 2. Let us say thatthe communication station A is capable of receiving beacons from thethree stations 0 through 2 within a super frame.

The beacon reception points-in-time of the nearby stations are describedas relative positions to the normal beacon of the local station in theNBOI field in bitmap format (described above). At the communicationstation A, the NBOI fields of the three beacons received from the nearbystations are shifted according to the reception point-in-time of thebeacons so as to match the corresponding position of bits on the timeaxis, and the OR is obtained of the NBOI bits for each timing forreference.

The sequence obtained as a result of integrating and referencing theNBOI files of the nearby stations is indicated by “OR of NBOIs” in FIG.16. 1 indicates the relative position of a timing regarding which a TBTThas already been set in the super frame, and 0 indicates the relativeposition of a timing regarding which a TBTT not yet been set. In theexample shown in the drawing, the sequence is “1111,1111,1111,1111”,i.e., all timings in the super frame have been marked, indicating thatthere are no more available TBTTs.

In such a case, the communication station A makes reference to the TYPEfields in the beacons received within the super frame, and obtains thepriority of the traffic of each. The communication station finds beaconsto which a priority lower than the order of preference of the trafficwhich it is attempting to transmit is set, and clears the bit in the “ORof NBOI” corresponding to the reception point-in-time of such alow-priority beacon.

With the example shown in FIG. 18, let us say that the TYPE of Beacon-0′has been set to a low order of preference. In this case, an Exclusive ORXOR is taken between the “Low Priority Beacon Rx” where the bit positioncorresponding to the beacon transmission timing for the low order ofpreference beacon is set to 1 and the “OR of NBOIs”, and the 5th bit,10th bit, and 12th bit, corresponding to the point-in-time where thebeacon-0′ is received in the “OR of NBOIs”, are cleared. Consequently,the sequence indicated by “XOR of Each” in the drawing is taken to bethe NBOI tally, and is taken as beacon transmission point-in-timecandidates for the communication station A. Subsequently, thecommunication station A can find an available TBTT according to theprocedures described above with reference to FIG. 9, and set the TBTTfor the new beacon.

As described above, performing processing procedures for eliminating abeacon with low order of preference from the NBOI and setting a TBTT fora new beacon for the local station means that the local station issetting the same TBTT as another station, and accordingly beaconcollision temporarily occurs. However, response is made to the collisionwithin the system to avoid collision, and accordingly the TBTT changingprocessing shown in FIG. 13 and FIG. 16 occur. Consequently, TBTTchanging processing is executed for low-priority beacons, andlow-priority beacons are gradually eliminated from the system.

FIG. 19 illustrates the way in which the communication stationeliminates beacons of other stations with low order of preference andsets a new TBTT, in a state wherein the super frame is already full ofbeacons for which TBTTs have been set. In the drawing, frompoint-in-time T0 to point-in-time T0′ represents one super frame, andthe upper tier, middle tier, and lower tier illustrate the time-sequencetransmission of the beacons over three super frames. Note that threecommunication stations, the STA0, the STA1, and the STA2 exist here,with at least the STA0 and the STA2 being within the range of reach ofairwaves so as to have a communication environment wherein signals canbe directly transmitted and received therebetween.

With the state shown at the upper tier in FIG. 19, the STA2 transmits inthe super frame a normal beacon (TYPE=255) and two auxiliary beaconswith order of preference (TYPE=) 127. Also, the STA0 transmits in thesuper frame a normal beacon (TYPE=255) and three auxiliary beacons withorder of preference (TYPE=) 254. The TBTT timings within the super frameare all occupied, and there are no available time spans.

Under such a situation, in the event that the STA0 wants to additionallytransmit two auxiliary beacons, the STA0 first performs a scanningoperation (not shown), and finds the auxiliary beacons transmitted bythe STA2 with the order of preference 127, as beacons having lower orderof preference than the beacons regarding which TBTTs are to be set bythe local station. Then, the Exclusive OR XOR of the “Low PriorityBeacon Rx) and “OR of NBOIs” is taken according to the proceduresdescribed with reference to FIG. 18, and the NBOI invalidates thetransmission timings of the auxiliary beacons from the STA2 and handlesthese as available TBTTs. Further, the STA0 determines to transmitauxiliary beacons with an order of preference of 254 at point-in-time T1and point-in-time T6 corresponding to the invalidated TBTT timings.

The middle tier in FIG. 19 illustrates the way in which the beacons ofthe STA0 and the STA2 are colliding, due to the STA0 transmitting theauxiliary beacons at point-in-time T1 and point-in-time T6. At thistime, the STA0 and the STA2 perform processing following TBTT changingprocedures shown in FIG. 13 or FIG. 16. Consequently, the STA2 which istransmitting auxiliary beacons with low order of preference starts theTBTT changing processing.

The STA2 performs a scanning operation to set TBTTs for the twoauxiliary beacons having the order of preference of 127, and searchesfor available time within the super frame (not shown), but no availabletime is found (or no auxiliary beacons with a lower order of preferenceare found), so the STA2 abandons transmitting of the auxiliary beacons.Accordingly, the situation settles down to that shown in the bottom tierin FIG. 19.

Repeating the above-described operations wherein the TBTTs of beaconswith low order of preference are eliminated from the super frame andTBTTs of beacons with high order of preference are set enables resourcesfor high priority to be ensured.

Now, the example described here is a case of containing newly-generatedhigh priority traffic, with high-priority traffic seizing the resourcesof low-priority traffic. There may be cases wherein a policy is insteadwherein TPPs already being serviced are given preference, regardless ofhow high or low the priority is. In such cases, the above processing forseizing low-priority TPPs is not activated, but in the event that atraffic group already being serviced falls into a collision state due tomoving of a communication station, there may be cases wherein one of theTPPs already being serviced must be eliminated. In such a case as well,high-priority traffic can be preferentially utilized by applyingprocedures the same as those described above.

H. Setting TBTT of Auxiliary Beacons Based on Priority (RemoteOperations)

According to the procedures described in Section G above, in the eventthat a communication station which transmits low-priority traffic existsnearby the communication station A which desires to set a TBTT for abeacon anew, the advantage can be obtained that resources for highpriority can be secured.

On the other hand, in the event that there are no communication stationswhich transmit low-priority traffic nearby the communication station A,and in the event that only communication stations which receivelow-priority traffic exist, the same cannot be eliminated. The reason isthat mutual beacon reception cannot be made with hidden terminals, andeven in the event that the communication station A invalidates thelow-priority traffic in the NBOI of the local station, this does notreach the hidden terminal side, so TBTT changing procedures such asshown in FIG. 13 and FIG. 16 cannot be directly activated.

Accordingly, in the event that the beacon transmission point-in-timestill cannot be found even with the means described with FIG. 18, thecommunication station which desires setting of a TBTT for a new beaconhas a nearby station to search for whether or not there is acommunication station transmitting low-priority traffic, and requeststopping of the transmission, thereby performing “remote operations” ofthe hidden terminal.

FIG. 20 and FIG. 21 illustrate the way in which a communication stationwhich desires setting of a TBTT for a new beacon stops transmission ofbeacons by remote operations via a nearby station, and sets a TBTT for alocal station beacon. In the drawing, from point-in-time T0 topoint-in-time T0′ represents one super frame, showing the sequencetransition of beacon transmission over four super frames. Also, acommunication environment is assumed here wherein three communicationstations, the STA0, the STA1, and the STA2 exist, with at least the STA0and the STA2 being out of the range of reach of airwaves, so thattransmission and reception of signals cannot be directly performed.

In the state shown at the top tier in FIG. 20, the STA2 is transmittinga normal beacon (TYPE=255) and five auxiliary beacons with an order ofpreference of (TYPE=) 2 within the super frame. Also, the STA0 and theSTA1 are each only transmitting normal beacons (TYPE=255) in the superframe. Thus, the TBTT timings within the super frame are all occupied.

Now, at point-in-time T0, the STA0 desires to transmit three auxiliarybeacons for transmitting traffic with an order of preference of 254, butrecognizes that the TBTT timings within the super frame are alloccupied. Further, even though the STA0 attempts to activate proceduresfor eliminating the low-priority traffic shown in FIG. 18, the auxiliarybeacon transmission timing cannot be found. Accordingly, the STA0describes information to the effect that “I want to transmit threebeacons with an order of preference of 254” in the ALERT field of thenormal beacon transmitted at point-in-time T0, and notifies this tosurrounding stations. The beacon in which such information is describedin the ALERT field is equivalent to a remote beacon stopping request tosurrounding stations. Also, following notification of the beacon stoprequest with the ALERT, the STA0 goes into a scan state for a while, tosearch for whether or not available slots can be created by remoteoperations with nearby stations.

Note that the ALERT field is a field for storing information to betransmitted to the nearby stations in an abnormal situation. In theabove descriptions the ALERT field is used for describing information tobe notified to the nearby stations that the local station is going tochange a TBTT. Here, the ALERT field has multiple definitions fornotifying multiple abnormal states. FIG. 22 schematically illustratesthe configuration of the ALERT field in this case. As shown in thedrawing, the ALERT field is sectioned into a type field which indicatesthe type of definition, and the main field for describing the abnormalstate. In the event that the type is changing of the TBTT of the localstation, information relating to the TBTT changing is described in themain field. Also, in the event of the type of a remote operation, theorder of preference of the beacons which the local station wants to setand the number of beacons are descried in the main field.

Upon receiving the beacon with information to the effect that “I want totransmit three beacons with an order of preference of 254” described inthe ALERT field, the STA1 performs a scanning operation for at least onesuper frame, in order to confirm whether or not there are beacons havingan order of preference below 254 being transmitted nearby. Simultaneouswith completion of the scan, the STA1 recognizes that the STA2 istransmitting five auxiliary beacons with a lower order of preference of2 in the super frame.

Next, as shown at the bottom tier in FIG. 20, the STA1 transmits abeacon stop request message M to the STA2 to the effect that “I want youto temporarily stop transmission of three beacons with an order ofpreference lower than the order of preference of 254”. During thiswhile, the STA0 remains in a scanning state to search for whether or notavailable slots can be created by remote operations with nearbystations.

In response to reception of the beacon stop request message M, the STA2stops transmission of the three auxiliary beacons transmitted atpoint-in-time T3, point-in-time T5, and point-in-time T7, of theauxiliary beacons with an order of preference of 2 that are beingcurrently transmitted.

Next, at the top tier in FIG. 21, the STA1 performs a scanning operationfor at least one frame, thereby detecting that point-in-time T3,point-in-time T5, and point-in-time T7, are available. Or, the fact thatpoint-in-time T3, point-in-time T5, and point-in-time T7, are available,is notified by the NBOI of a beacon transmitted by the STA2 or othernearby stations. Note that during this while, the STA0 remains in ascanning state to search for whether or not available slots can becreated by remote operations with nearby stations.

Next, at the bottom tier in FIG. 21, the STA0 makes reference to theNBOI of the beacon received from the STA1 or another nearby station, andupon recognizing that point-in-time T3, point-in-time T5, andpoint-in-time T7, are available, sets the TBTTs for the auxiliarybeacons each having order of preference of 254 at these timings, andstarts beacon transmission.

On the other hand, after stopping beacon transmission temporarily, theSTA2 searches for available TBTTs within the super frame to attemptauxiliary beacon transmission with an order of preference of 2 again.However, the STA0 is already occupying these time spans with beaconshaving a higher order of preference, so no available points-in-time canbe found, and auxiliary beacon transmission is abandoned.

Thus, performing remote operations for setting TBTTs for beacons withhigher order of preference by eliminating beacons with lower order ofpreference in the super frame enables resources to be secured for highpriority.

Note that a communication station, which has received information to theeffect that “I want to transmit a beacon with an order of preference ofXX” described in the ALERT field, performs beacon stopping processing bythe above-described remote operations, and also temporarily stopstransmission processing of auxiliary beacons of itself lower than theorder of preference of XX indicated.

INDUSTRIAL APPLICABILITY

The present invention has been described in detail with reference toparticular embodiments. However, it is self-evident that one skilled inthe art can be various modifications and substitutions to theembodiments without departing from the essence of the present invention.

With the present specification, in an autonomously-dispersed wirelessnetwork, the present invention has been described with primaryembodiments in application to a communication environment whereincommunication stations each notify each other with beacons atpredetermined frame cycles, but the essence of the present invention isnot restricted to this.

For example, the present invention can be similarly applied to acommunication system of another arrangement wherein beacons aretransmitted from multiple communication stations within communicationrange, or to a communication system of another arrangement wherein eachcommunication station operates in predetermined tame intervalincrements, so as to perform signal processing by periodically settingbands using reservation or preferentially, for each of the timeintervals.

In conclusion, the present invention has been disclosed in the form ofexamples, and the descriptions in the present specification are not tobe interpreted restrictively. The Claims should be referenced todetermine the essence of the present invention.

REFERENCE NUMERALS

-   -   100 wireless communication device    -   101 interface    -   102 data buffer    -   103 central control unit    -   104 beacon generating unit    -   106 wireless transmission unit    -   107 timing control unit    -   109 antenna    -   110 wireless reception unit    -   112 beacon analyzing unit    -   113 information storage unit

The invention claimed is:
 1. A wireless communication device comprising:a communication circuit configured to transmit and receive wirelessdata; and processing circuitry configured to generate beacon signalsrelating to a first communication station; analyze beacon signalsreceived by said communications circuit from a second communicationstation; detect a collision between a first beacon transmission timingof the beacon signals relating to the first communication station and asecond beacon transmission timing of beacon signals relating to thesecond communication station; and change the first beacon transmissiontiming when the collision is detected and the timing of the first beacontransmission timing is later than a timing of the second beacontransmission timing.
 2. The wireless communication device of claim 1,wherein the communication circuit transmits a notification to nearbystations prior to the processing circuitry changing the first beacontransmission timing using a time interval allocated for a beacon of thefirst communication station.
 3. A wireless communications methodcomprising: generating, by processing circuitry, beacon signals relatingto a first communication station; receiving, by a communication circuit,beacon signals transmitted from a second communication station;analyzing, by the processing circuitry, the beacon signals received fromthe second communication station; detecting, by the processingcircuitry, a collision between a first beacon transmission timing of thebeacon signals relating to the first communication station and a secondbeacon transmission timing of beacon signals relating to the secondcommunication station; and changing, by the processing circuitry, thefirst beacon transmission timing when the collision is detected and thetiming of the first beacon transmission timing is later than the timingof the second beacon transmission timing.
 4. The method of claim 3,further comprising: transmitting, by the communication circuit, anotification to nearby stations prior to the processing circuitrychanging the first beacon transmission timing using a time intervalallocated for a beacon of the first communication station.
 5. A wirelesscommunication system comprising: a first communication station; and afirst communication device including a communication circuit andprocessing circuitry, the communication circuit configured to transmitand receive wireless data and the processing circuitry configured togenerate beacon signals relating to the first communication station,analyze beacon signals received by said communications circuit from asecond communication station, detect a collision between a first beacontransmission timing of the beacon signals relating to the firstcommunication station and a second beacon transmission timing of beaconsignals relating to the second communication station, and change thefirst beacon transmission timing when the collision is detected and thetiming of the first beacon transmission timing is later than a timing ofthe second beacon transmission timing.
 6. The system of claim 5, whereinthe communication circuit transmits a notification to nearby stationsprior to the processing circuitry changing the first beacon transmissiontiming using a time interval allocated for a beacon of the communicationstation.
 7. The wireless communication device of claim 1, wherein thecommunication circuit transmits a request to nearby stations to changethe second beacon transmission timing using a time interval allocatedfor a beacon of the second communication station.
 8. The wirelesscommunication device of claim 1, wherein the processing circuitry isfurther configured to determine a priority difference between the beaconsignals relating to the first communication station and the beaconsignals relating to the second communication station.
 9. The wirelesscommunication device of claim 8, wherein the processing circuitry isfurther configured to change the first beacon transmission timing when apriority of the beacon signals relating to the first communicationstation is lower than a priority of the beacon signals relating to thesecond communication station.
 10. The wireless communication method ofclaim 3, further comprising: transmitting, by the communication circuit,a request to nearby stations to change the second beacon transmissiontiming using a time interval allocated for a beacon of the secondcommunication station.
 11. The wireless communication method of claim 3,further comprising: determining, by the processing circuitry, a prioritydifference between the beacon signals relating to the firstcommunication station and the beacon signals relating to the secondcommunication station.
 12. The wireless communication method of claim11, further comprising: changing, by the processing circuitry, the firstbeacon transmission timing when a priority of the beacon signalsrelating to the first communication station is lower than a priority ofthe beacon signals relating to the second communication station.
 13. Thewireless communication system of claim 5, wherein the communicationcircuit transmits a request to nearby stations to change the secondbeacon transmission timing using a time interval allocated for a beaconof the second communication station.
 14. The wireless communicationsystem of claim 5, wherein the processing circuitry is furtherconfigured to determine a priority difference between the beacon signalsrelating to the first communication station and the beacon signalsrelating to the second communication station.
 15. The wirelesscommunication device of claim 14, wherein the processing circuitry isfurther configured to change the first beacon transmission timing when apriority of the beacon signals relating to the first communicationstation is lower than a priority of the beacon signals relating to thesecond communication station.